Utas190812a

[GregUtas]

Mostly parser enhancements:

• Support wchar_t, char16_t, and char32_t as keywords.
• Support character escape sequences (\, \x, \u, \U).
• Support encoding tag prefixes (u8, u, U, L) for character and string literals.
• Support alias types (using <name> = <TypeSpec>).
• Allow flexible ordering of keyword tags used in function and data declarations/definitions.
• Don't flag a deleted function with ItemCouldBePrivate.
• Don't flag a direct template parameter with MemberInitMissing.
• Use class instead of typename when a template parameter should be a class.

Modifies #66.