parse: flesh things out somewhat

Signed-off-by: Drew DeVault <sir@cmpwn.com>

parse: initial AST types

lex: implement quoted words

lex: add 'case' token

lex: drop 'not', add 'else'

lex: remove heredocs

We'll implement these in the parser instead.

lex: implement keywords

lex: lex line feed as a token

lex: expand word test

lex: implement unquoted word lexing

lex: drop "extra" tokens for now

Expand lexer

lex: initial riggings

Initial commit