0.21.0

There are three features added in Unidoc 0.21.0.

• Declarations that are overloaded on async can now be disambiguated in the UCF syntax with [async], or [async: false] to select the non-async overload.
• Unidoc can now conditionally ignore broken symbol links using the [ignore when: SOME_DEFINITION] syntax, which can be combined with --define SOME_DEFINITION passed to unidoc compile. This is most useful for CI workflows that attempt to validate documentation that includes links to symbols that only exist on certain platforms.
• You can now print the tool version with unidoc --version

Full Changelog: 0.20.1...0.21.0