Switch anstyle-roff to anstyle-parse

[epage]

With #4, we can now use our own parser. We might need to reuse some code from anstyle-stream to do so.

[Calder-Ty]

Hey I saw this, and saw the work you did forking vte. With the transfer of the
Roff style code were you thinking of a general purpose bytes or str to anstyle or just
implement one for the roff crate for now?

[epage]

Yes, I think it could make sense to make the conversion generic since roff will likely need everything that an anstyle parser would need.

anstyle-stream has a subset of bytes to anstyle used, just enough to get wincon working. That could be generalized. I lean towards that living in anstyle_parse or anstyle_stream. No preference yet on which of those it should be in.

This also isn't the most critical of things; I just didn't want to lose track of this.