Improve highlighting of bare and raw strings, and add missing unit & operators

[LemmusLemmus]

• Added µs as a valid unit.
• Added the new operators like and not-like.
• Disallowed semicolon in bare strings (this should also fix Syntax highlighting breaks for defs with multiple commands separated by ; (semicolon) #190)
• Allowed # in bare strings (except for the first character, since then it is a comment and not a bare string).
• Prioritized raw string highlighting over commands and bare strings (in e.g. r'#str#', r should not be highlighted as a command).

Sidenotes

• Technically, commas should also be allowed in bare strings. However, commas can only be in some bare strings, since if the bare string is inside a list, then commas should not be recognized as part of the bare string: [bare,strings]. Hence, I have left commas disallowed as they were before.
• The new operators like and not-like are missing from the Nushelll operators documentation currently...
• Regarding a better regex for comments, I realized that the rules for when a comment is allowed without white-space in behind it is quite convoluted, so I have left it untouched.

[fdncred]

Thanks