Game plan:
 * finish regexps (interpol in r.e. literal)
 * attr_*
 * *_eval
 * MRI compatibility layer
 * working GC
 
Shorter term problems:
 * catch/throw
 * Float range is small
 * RubyClass::new_instance(): these should not be centralised
 * assignments should always return rvalue
 * Fixnum, Symbol don't have instance variables
 * flex encounters push-black overflows due to brace nesting occasionally
 * Module::method syntax
 * '`' method impossible to declare due to lexer switching modes
 * Dir::glob needs to work to MRI's wildcard syntax
 * and/&&, or/|| need to not evaulate second condition if first fails/succeeds
 * `p 1 and 2' should parse to `(p 1) and 2'
 * if we `def a(b); end', then just `a' should raise an ArgumentError of not enough arguments
 * expand hash-style on end to hash last argument
 * optional argument def a(b=(anything; can(); go = here)) syntax needs to work
 * finish fixing the edge cases when parser encounters syntax error causes memory leak (valgrind)