REGEX ENGINE

I've thought for a while it would be fun and interesting to write my
own regular expression engine using Thompson's construction algorithm,
so here we are.

                               Grammar

This engine is not going to be strictly supporting any standard
syntax; the expression syntax I intend to support follows.

	regex ::= sequence ( '|' regex )?
	sequence ::= term+
	term ::= ( '.' | class | literal | '(' regex ')' ) quantifier?
	class ::= '[' '^'? literal+ ']'
	literal ::= non-special | '\' special
	quantifier ::= '*' | '+' | '?'
	special ::= quantifier | '|' | '(' | ')' | '[' | ']' | '^' | '\'