Fix use of # character in Racket lexer

[pyrmont]

The # character can be used in Racket in multiline comments as well as in boolean constants. As described in #1471, the Racket lexer does not at present correctly lex multiline comments or full-word (i.e. #true as opposed to #t) boolean constants.

This PR fixes those bugs (and will close #1471). It also removes extraneous code from the visual sample.

[pyrmont]

How's this look @yugenekr?

[yugaego]

Hi @pyrmont, thank you for working on this.

The updates you provided look mostly fine to me (I'm not Ruby or Rouge person) in regard the particular use cases I provided.

If to dive into a bit more details, more use cases might need to be covered.

I believe Racket parser documentation provides the list of all # use cases.
For example, it mentions the uppercase #T and #F also should be treated as booleans. (I'm not aware if the matching rules are case-insensitive.)

Also, see several comments examples from this documentation page

This section might add some context to the Racket comments usage:
https://docs.racket-lang.org/style/Choosing_the_Right_Construct.html?q=comments#%28part._.Comments%29

Do you think it could be worthwhile working on the rest of the cases? Or keep it till the exact need arises?

[pyrmont]

@yugenekr I think having support for commenting out s-expressions would be cool (and I don't think too difficult). Will have to add another state but should be straightforward. I'll have a tinker.

[pyrmont]

@yugenekr Famous last words, I guess. I realised looking at the list of datums in Racket that it could actually get quite complicated. I've tried a relatively simple approach that I think will cover most cases. How does it look to you?

[yugaego]

I agree these changes should be sufficient for now.
Other cases may be covered when needed.
Thanks!

[yugaego]

Minor notice. I'm not aware of exact usages of these samples. And from my perspective it might be more descriptive to use doc comments such as: ;; Highlight booleans, (...) should be highlighted as the commented text or similar.

[pyrmont]

@yugenekr Thanks for your help on this one. The update version will go out as part of the next release of Rouge. That's scheduled for Tuesday 14 April 🎉

[yugaego]

Great! Thanks a lot reacting fast with the updates.