Documentation cleanup.
Added missing fixture.
Renamed capabilities to libgit2-capabilities.
More documentation cleanups.
Fixed typo.
Fixed behaviour of list-objects 'tag so it no longer jumps to the target.  This means that lightweight tags will now work as expected.
Added better tag semantics and added some more tag documentation.
Cleaned up tag documentation.
Added get-object function for tags, simplified list-objects to use it. Also improved tag documentation.
Updated references documentation.
Fixed 2 failing tests.