some cleanup in the structure

Added some subfolders, and moved several files for better compatibility
with setuptools.

Moved the word addin in the "bin" directory, with an aditionnal
installer.cfg file. This installer will be used for distributing the
addin with pynsist (see https://github.com/takluyver/pynsist).

Cleaned up the "doccleaner.py" file, mainly for better compatibilty with
pynsist.