Ch8 Finale task definition

[skaunov]

Can we improve task definition so that limitations would be obvious from the start? It's my bad, I wasn't reading thorough enough, but staring long enough at Matcher::new signature output I decided that there's no way it could return None. Implemented it the way unmatched parenthesis go to RawText(_), and of course smashed into broken_matcher() test.

It's just a piece of feedback... Do you feel like that this detail deserve few words in the chapter?

[skaunov]

Still not clear for example what Option should be return for ")(d|e)" string.

I finished a Gist to illustrate the path which lead me to some frustration. X) I started to suspect that it will end that way when new returned Some(..) for Option whenever. But here it is! If you (or others!) would give a review to the Gist on related or unrelated topics it would be really appreciated!

PS Praise to Ff and Gh which were saving draft of this comment from May!