Lex Type, Identifiers in additional contexts

[sifton]

So I've made a couple enhancements that noticeably improve syntax highlighting, particularly for VSCode:

• Modified the type rule to match only those lexemes which start with an ASCII capital letter (e.g. Vertex but not vertex, PartialEq but not partialEq).
• Added an identifier rule which accepts everything that type used to accept, but is matched later so as not to conflict
• Allow types and identifiers to be matched in attributes, function definitions, and elsewhere (not otherwise specified)

Hope this is cool.