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.
Merge pull request #24 from nathanaeljones/fix-c-closure-coroutines

provide stack/state to Ruby functions