Add type overloads for zip_equal and zip_offset
Add type overloads for zip_equal and zip_offset

This follows the standard-library type definitions[1,2] for `zip` that
have special overloads for cases with 1-5 arguments, and a fallback
overload for 6 or more arguments (which also applies if called with
explicit varargs).

[1] https://github.com/python/typeshed/blob/master/stdlib/builtins.pyi#L1310
[2] https://github.com/python/typeshed/blob/master/stdlib/%40python2/builtins.pyi#L1030

erikrose/more-itertools,more-itertools/more-itertools