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().
Add long int implementation using C long long type, enable for unix port.
Implement LOAD_CONST_INT (by dispatching to int object implementation).