docs: update for v1.0.0

CHANGES.md

@@ -1,5 +1,19 @@
 # Changes
 
+## Version 1.0.0
+- The library now follows semantic versioning as per https://semver.org/.
+- Elements support is now enabled by default, reflecting the common library
+  usage. Please see the `configure --help` entries for `--disable-elements`
+  and `--disable-elements-abi` for details.
+- The ABI of the library is now consistent by default regardless of whether
+  it is built with or without Elements support.
+- When configured to build as a static library, linking to libwallycore.a
+  requires additionally linking to libsecp256k1.a.
+- Wally can now be configured to build against a system-wide libsecp256k1.
+- Some functions in the c++ header wally.hpp have changed interface slightly.
+  Note that this header is deprecated and will be replaced in an upcoming
+  release with higher level wrappers in the same manner as Python and JS.
+
 ## Version 0.9.1
 - PSET: When adding an Elements transaction output to a PSET, the nonce
   commitment was incorrectly mapped to the PSET output blinding key field.

README.md

@@ -5,7 +5,7 @@ for cryptocurrency wallets.
 
 Read the API documentation at https://wally.readthedocs.io.
 
-Note that library interfaces may change slightly while the library design matures. Please see the [CHANGES](./CHANGES.md) file to determine if the API has changed when upgrading.
+Please see the [CHANGES](./CHANGES.md) for details of ABI changes when upgrading.
 
 Please report bugs and submit patches to [Our github repository](https://github.com/ElementsProject/libwally-core). If you wish to report a security issue, please read [Our security reporting guidelines](./SECURITY.md).
 
@@ -88,6 +88,8 @@ $ brew install swig
    header files. This option *must not be given if wally is being installed as a system/shared library*. (default: no).
 - `--enabled-standard-secp`. Excludes support for features that are unavailable in
    the standard [libsecp256k1 library](https://github.com/bitcoin-core/secp256k1).
+- `--with-system-secp256k1=<package_name>`. Compile and link against a system-wide
+   install of libsecp256k1 instead of the in-tree submodule. (default: not enabled).
 - `--enable-mbed-tls`. Use mbed-tls hashing functions if available. This typically
    results in faster hashing on embedded platforms such as STM32. Note that the user
    must define `MBEDTLS_SHA256_ALT` and/or `SOC_SHA_SUPPORT_PARALLEL_ENG` matching the