[skip ci] add CHANGELOG entries for old point releases.

I opted to preserve explicit entries for backports in both the original
feature release and the backported point release, rather than trying to
pretend that the releases were actually sequential.

Also, remove some empty subsections from the file.

CHANGELOG.md

@@ -385,6 +385,30 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Removed `SigevNotify` on OpenBSD and Redox.
   (#[1511](https://github.com/nix-rust/nix/pull/1511))
 
+## [0.22.3] - 22 January 2022
+### Changed
+- Relaxed the bitflags requirement from 1.3.1 to 1.1.  This partially reverts
+  #1492.  From now on, the MSRV is not guaranteed to work with all versions of
+  all dependencies, just with some version of all dependencies.
+  (#[1607](https://github.com/nix-rust/nix/pull/1607))
+
+## [0.22.2] - 28 September 2021
+### Fixed
+- Fixed buffer overflow in `unistd::getgrouplist`.
+  (#[1545](https://github.com/nix-rust/nix/pull/1545))
+- Added more errno definitions for better backwards compatibility with
+  Nix 0.21.0.
+  (#[1467](https://github.com/nix-rust/nix/pull/1467))
+
+## [0.22.1] - 13 August 2021
+### Fixed
+- Locked bitflags to < 1.3.0 to fix the build with rust < 1.46.0.
+
+### Removed
+- Removed a couple of termios constants on redox that were never actually
+  supported.
+  (#[1483](https://github.com/nix-rust/nix/pull/1483))
+
 ## [0.22.0] - 9 July 2021
 ### Added
 - Added `if_nameindex` (#[1445](https://github.com/nix-rust/nix/pull/1445))
@@ -410,8 +434,19 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   `nix::Error::EINVAL`.
   ([#1446](https://github.com/nix-rust/nix/pull/1446))
 
+## [0.21.2] - 29 September 2021
+### Fixed
+- Fixed buffer overflow in `unistd::getgrouplist`.
+  (#[1545](https://github.com/nix-rust/nix/pull/1545))
+
+## [0.21.1] - 13 August 2021
 ### Fixed
+- Locked bitflags to < 1.3.0 to fix the build with rust < 1.46.0.
+
 ### Removed
+- Removed a couple of termios constants on redox that were never actually
+  supported.
+  (#[1483](https://github.com/nix-rust/nix/pull/1483))
 
 ## [0.21.0] - 31 May 2021
 ### Added
@@ -467,6 +502,20 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Removed some Errno values from platforms where they aren't actually defined.
   (#[1452](https://github.com/nix-rust/nix/pull/1452))
 
+## [0.20.2] - 28 September 2021
+### Fixed
+- Fixed buffer overflow in `unistd::getgrouplist`.
+  (#[1545](https://github.com/nix-rust/nix/pull/1545))
+
+## [0.20.1] - 13 August 2021
+### Fixed
+- Locked bitflags to < 1.3.0 to fix the build with rust < 1.46.0.
+
+### Removed
+- Removed a couple of termios constants on redox that were never actually
+  supported.
+  (#[1483](https://github.com/nix-rust/nix/pull/1483))
+
 ## [0.20.0] - 20 February 2021
 ### Added
 
@@ -530,8 +579,6 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1278](https://github.com/nix-rust/nix/pull/1278))
 - Made `unistd::fork` an unsafe funtion, bringing it in line with [libstd's decision](https://github.com/rust-lang/rust/pull/58059).
   (#[1293](https://github.com/nix-rust/nix/pull/1293))
-### Fixed
-### Removed
 
 ## [0.18.0] - 26 July 2020
 ### Added
@@ -644,22 +691,16 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Added
 - Add `CLK_TCK` to `SysconfVar`
   (#[1177](https://github.com/nix-rust/nix/pull/1177))
-### Changed
-### Fixed
 ### Removed
 - Removed deprecated Error::description from error types
   (#[1175](https://github.com/nix-rust/nix/pull/1175))
 
 ## [0.16.1] - 23 December 2019
-### Added
-### Changed
 ### Fixed
 
 - Fixed the build for OpenBSD
   (#[1168](https://github.com/nix-rust/nix/pull/1168))
 
-### Removed
-
 ## [0.16.0] - 1 December 2019
 ### Added
 - Added `ptrace::seize()`: similar to `attach()` on Linux
@@ -787,8 +828,6 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Enabled `sched_yield` for all nix hosts.
   ([#1090](https://github.com/nix-rust/nix/pull/1090))
 
-### Removed
-
 ## [0.14.1] - 2019-06-06
 ### Added
 - Macros exported by `nix` may now be imported via `use` on the Rust 2018
@@ -813,8 +852,6 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Fix the build on Android and Linux/mips with recent versions of libc.
   ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
 
-### Removed
-
 ## [0.14.0] - 2019-05-21
 ### Added
 - Add IP_RECVIF & IP_RECVDSTADDR. Enable IP_PKTINFO and IP6_PKTINFO on netbsd/openbsd.
@@ -883,6 +920,23 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   should've been defined in the first place.
   ([#1055](https://github.com/nix-rust/nix/pull/1055))
 
+## [0.13.1] - 2019-06-10
+### Changed
+- Changed some public types from reexports of libc types like `uint32_t` to the
+  native equivalents like `u32.`
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+
+### Fixed
+- Fix the build on Android and Linux/mips with recent versions of libc.
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+- Fixed build on Linux/arm and Linux/s390x with the latest Rust libc
+  ([52102cb](https://github.com/nix-rust/nix/commit/52102cb76398c4dfb9ea141b98c5b01a2e050973))
+
+### Removed
+- `Daemon`, `NOTE_REAP`, and `NOTE_EXIT_REPARENTED` are now deprecated on OSX
+  and iOS.
+  ([#1033](https://github.com/nix-rust/nix/pull/1033))
+
 ## [0.13.0] - 2019-01-15
 ### Added
 - Added PKTINFO(V4) & V6PKTINFO cmsg support - Android/FreeBSD/iOS/Linux/MacOS.
@@ -900,14 +954,30 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Added an `mprotect` wrapper.
   ([#991](https://github.com/nix-rust/nix/pull/991))
 
-### Changed
 ### Fixed
 - `lutimes` never worked on OpenBSD as it is not implemented on OpenBSD. It has
   been removed. ([#1000](https://github.com/nix-rust/nix/pull/1000))
 - `fexecve` never worked on NetBSD or on OpenBSD as it is not implemented on
   either OS. It has been removed. ([#1000](https://github.com/nix-rust/nix/pull/1000))
 
+## [0.12.1] 2019-06-08
+### Changed
+- Changed some public types from reexports of libc types like `uint32_t` to the
+  native equivalents like `u32.`
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+
+### Fixed
+- Fix the build on Android and Linux/mips with recent versions of libc.
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+- Fixed build on Linux/arm and Linux/s390x with the latest Rust libc
+  ([52102cb](https://github.com/nix-rust/nix/commit/52102cb76398c4dfb9ea141b98c5b01a2e050973))
+
 ### Removed
+- `fexecve` never worked on NetBSD or on OpenBSD as it is not implemented on
+  either OS. It has been removed. ([#1000](https://github.com/nix-rust/nix/pull/1000))
+- `Daemon`, `NOTE_REAP`, and `NOTE_EXIT_REPARENTED` are now deprecated on OSX
+  and iOS.
+  ([#1033](https://github.com/nix-rust/nix/pull/1033))
 
 ## [0.12.0] 2018-11-28
 
@@ -959,7 +1029,24 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Fixed passing multiple file descriptors over Unix Sockets.
   ([#918](https://github.com/nix-rust/nix/pull/918))
 
+## [0.11.1] 2019-06-06
+### Changed
+- Changed some public types from reexports of libc types like `uint32_t` to the
+  native equivalents like `u32.`
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+
+### Fixed
+- Fix the build on Android and Linux/mips with recent versions of libc.
+  ([#1072](https://github.com/nix-rust/nix/pull/1072/commits))
+- Fixed build on Linux/arm and Linux/s390x with the latest Rust libc
+  ([52102cb](https://github.com/nix-rust/nix/commit/52102cb76398c4dfb9ea141b98c5b01a2e050973))
+
 ### Removed
+- `fexecve` never worked on NetBSD or on OpenBSD as it is not implemented on
+  either OS. It has been removed. ([#1000](https://github.com/nix-rust/nix/pull/1000))
+- `Daemon`, `NOTE_REAP`, and `NOTE_EXIT_REPARENTED` are now deprecated on OSX
+  and iOS.
+  ([#1033](https://github.com/nix-rust/nix/pull/1033))
 
 ## [0.11.0] 2018-06-01