NEW: py-unitypy - extractor for Unity projects, with deps

Hi,

I started using UnityPy for a project and it would be useful to see
about adding it to ports. It essentially allows accessing the assets of
Unity projects. I've included 4 of the 5 dependencies in the
attachments: py-brotli, py-lz4, py-fsb5, py-texture2ddecoder. The last
one is py-Pillow and is already in ports.

A relatively simple example is on the project GitHub page:
https://github.com/K0lb3/UnityPy#example

I've tested this and it works, and will probably be using it regularly
in the near future.

This project and most dependencies are MIT-licensed. The only exception
is py-lz4, which is BSD 3-clause.

Some notes on the ports:
- py-brotli build a bundled version and doesn't provide a way that I
could find to link to system libs from archivers/brotli.
- py-texture2ddecoder needs swap16() and swap32() to be commented out,
as it clashes with a definition in a header. Also had to work around
malloc_usable_size, but this seems to work.

ok? comments?