Document per-item versions using @since gates

wit/monotonic-clock.wit

@@ -7,35 +7,45 @@ package wasi:[email protected];
 ///
 /// A monotonic clock is a clock which has an unspecified initial value, and
 /// successive reads of the clock will produce non-decreasing values.
+///
+/// It is intended for measuring elapsed time.
+@since(version = 0.2.0)
 interface monotonic-clock {
     use wasi:io/poll@0.2.0.{pollable};
 
     /// An instant in time, in nanoseconds. An instant is relative to an
     /// unspecified initial value, and can only be compared to instances from
     /// the same monotonic-clock.
+    @since(version = 0.2.0)
     type instant = u64;
 
     /// A duration of time, in nanoseconds.
+    @since(version = 0.2.0)
     type duration = u64;
 
     /// Read the current value of the clock.
     ///
     /// The clock is monotonic, therefore calling this function repeatedly will
     /// produce a sequence of non-decreasing values.
+    @since(version = 0.2.0)
     now: func() -> instant;
 
     /// Query the resolution of the clock. Returns the duration of time
     /// corresponding to a clock tick.
+    @since(version = 0.2.0)
     resolution: func() -> duration;
 
     /// Create a `pollable` which will resolve once the specified instant
-    /// has occurred.
+    /// occured.
+    @since(version = 0.2.0)
     subscribe-instant: func(
         when: instant,
     ) -> pollable;
 
-    /// Create a `pollable` that will resolve after the specified duration has
-    /// elapsed from the time this function is invoked.
+    /// Create a `pollable` which will resolve once the given duration has
+    /// elapsed, starting at the time at which this function was called.
+    /// occured.
+    @since(version = 0.2.0)
     subscribe-duration: func(
         when: duration,
     ) -> pollable;

wit/wall-clock.wit

@@ -13,8 +13,10 @@ package wasi:[email protected];
 /// monotonic, making it unsuitable for measuring elapsed time.
 ///
 /// It is intended for reporting the current date and time for humans.
+@since(version = 0.2.0)
 interface wall-clock {
     /// A time and date in seconds plus nanoseconds.
+    @since(version = 0.2.0)
     record datetime {
         seconds: u64,
         nanoseconds: u32,
@@ -33,10 +35,12 @@ interface wall-clock {
     ///
     /// [POSIX's Seconds Since the Epoch]: https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap04.html#tag_21_04_16
     /// [Unix Time]: https://en.wikipedia.org/wiki/Unix_time
+    @since(version = 0.2.0)
     now: func() -> datetime;
 
     /// Query the resolution of the clock.
     ///
     /// The nanoseconds field of the output is always less than 1000000000.
+    @since(version = 0.2.0)
     resolution: func() -> datetime;
 }

wit/world.wit

@@ -1,6 +1,9 @@
 package wasi:clocks@0.2.0;
 
+@since(version = 0.2.0)
 world imports {
+    @since(version = 0.2.0)
     import monotonic-clock;
+    @since(version = 0.2.0)
     import wall-clock;
 }