Add the revsets mutable and immutable.

I add them as aliases, since a user may instead choose to define `immutable_heads()`, for example, as `heads(immutable())`, and the define `immutable()` instead.

CHANGELOG.md

@@ -29,6 +29,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `ui.color = "debug"` prints active labels alongside the regular colored output.
 
+* Added new revsets `mutable()` and `immutable()`.
+
 ### Fixed bugs
 
 * When the working copy commit becomes immutable, a new one is automatically created on top of it 

cli/src/config/revsets.toml

@@ -18,3 +18,5 @@ latest(
 '''
 
 'immutable_heads()' = 'trunk() | tags()'
+'immutable()' = '::immutable_heads()'
+'mutable()' = '~immutable()'

docs/revsets.md

@@ -219,6 +219,10 @@ for a comprehensive list.
 
 * `immutable_heads()`: Resolves to `trunk() | tags()` by default. See
   [here](config.md#set-of-immutable-commits) for details.
+* `immutable()`: Resolves to `::immutable_heads()` by default. See
+  [here](config.md#set-of-immutable-commits) for details.
+* `mutable()`: Resolves to `~immutable()` by default. See
+  [here](config.md#set-of-immutable-commits) for details.
 
 
 ## The `all:` modifier