Substantial improvements to String doc

[NotTheDr01ds]

Changes:

• First and foremost, documents raw strings
• Overview table now provides links to the sections themselves with more detail
• Drastically reworked backtick-quoted string section, as the existing doc related these to single-quoted strings. In actually, these are bare-word strings that allow spaces.
• Miscellaneous grammar and phrasing improvements.

I'll come back and revisit the bare-word string section (and more) later, but I do need to get this committed so that I can reference raw strings in a separate PR ;-)

[fdncred]

Thanks for updating these. Mostly looks good. Just a couple comments above.

[NotTheDr01ds]

Thanks - both good catches. Updated both.

[fdncred]

Thanks