Updated repo URL to point to GH.
Renamed CHANGES --> CHANGES.rst

And fixed setup.py which was broken since README rename.
Add same-codebase support for python 2.7.

When I opted for two codebases for python2/python3,
Send2Trash used C modules and it was easier to just have two
packages. With the ctypes version, supporting both python
versions becomes trivial and it's much more convenient to
merge them back into a single codebase.

I've only tested this code on Linux. I've converted plat_osx and
plat_win, but they only work theoretically.