Documentation for ctypes.

Documentation for ctypes.
I think that 'generic operating system services' is the best category.
Note that the Doc/lib/libctypes.latex file is generated from reST sources.
You are welcome to make typo fixes, and I'll try to keep the reST sources
in sync, but markup changes would be lost - they should be fixed in the tool
that creates the latex file.
The conversion script is external/ctypes/docs/manual/mkpydoc.py.