Document version availability for each language extension
A certain amount of "historical" information about language extensions is of sufficient practical utility to deserve a place in the GHC documentation. I believe that the documentation for each language extension should include
- The GHC version in which it first appeared.
- Any major changes that have been made to the extension since the previous major-major version. For example, the GHC 8.x.x documentation for any given language extension should include any major changes to it since 7.0.1.
At present, the only way I see to get this information is to dig through previous versions of the documentation and change logs, which is rather inefficient.