Support raw strings

[LemmusLemmus]

This pull request adds syntax highlighting for raw strings (#196) and autoClosingPairs.

Implementation notes

• Since autoClosingPairs does not seem to support regex open/close, I have had to repeat a couple of possible raw string pairs. One could add more...
• The current highlight color chosen (for r, # and the string itself) is of course opinionated. I just choose that which I found easiest to implement.
• I have not added the condition "notIn": ["comment"], because while typing a raw string, one enters a comment r#, and the notIn would therefore always fail. This could be changed however, depending on question 3. below.

Questions

1. Some raw string examples should probably be included in example.nu, however that file is generated and so I do not know how the example strings should be added.
2. Unrelated, but what is the autoClosingPair /** */ used for in the Nushell language?
3. Also unrelated, but I noticed that the syntax highlighting of e.g.

   echo hello#there

   is also wrong. #there is not considered as a comment by Nushell, but rather as a part of (in this case) the bare string. For a comment to actually be a comment, I think that there must be either a new line or white-space before it, i.e. by replacing the current regex "match": "(#.*)$" with "match": "(?<=^|\\s)(#.*)$".

[fdncred]

Thanks for the PR.

Unrelated, but what is the autoClosingPair /** */ used for in the Nushell language?

no clue. probably shouldn't be there.

is also wrong. #there is not considered as a comment by Nushell

sounds like a bug

[fdncred]

seems good enough to me. thanks!

[LemmusLemmus]

Would you appreciate another PR for removing the /** and changing the comment regex?

[fdncred]

sure