Extype

Once again, more fixes and patches.

This version brings some new built-in extensions and fixes.

* New `str` extensions `to_int` and `to_float`.
* Fix but where installation on Windows wouldn't work.

The very first release of the `extype` Python package!

This release has the basic features of the package:
* Allow extending types via other types.
* Provided useful extensions for some of the built-in types.