Eat up comments instead of calling them parse error:
* in @keyframe declaration #2059,
* after rule name before semicolon #826.

The comments are eaten instead of being printed into output, but it is
better then crashing on them.
tt
Merge pull request #2169 from SomMeri/comments-keyframe-rule

Accept comments in @keyframe and after rule name - merging for next patch release.