Merge pull request #197 from pfalcon/mod-singletons

Implement modules as singletons Python semantics.
Properly print MP_OBJ_QSTR objects.
Pre-create sys module.
unix: Implement sys.argv.
Add MP_OBJ_TYPE(o) accessor.

Should not be overused, but when needed, it's needed.
rt_is_true(): Start with testing for (expected) boolean values.
Add rt_resolve_method() which doesn't throw exception if method not found.

Unlike previosuly existing rt_load_method().