Add a spec that verifies ruby code is successfully called within a coroutine.
Add a failing spec where we pass arguments to a Ruby function within a co-routine. Suprising error suggests all co-routine related work may be fixable.
Fixes #19. C closures now use the lua state provided to them instead of the state they were defined in. This allows them to operate correctly from coroutines.
Use null-safe string method for symbols as well as strings.
Use more performant .bytesize instead of unpack('C*').size.
Add spec demonstrating failure when a symbol contains a null character.
Add more (perhaps redundant) specs to string_spec.