Fix doctest example.
Mention in the tutorial that 'errcheck' is explained in the ref manual.
Use better wording in some places.
Remoce code examples that shouldn't be in the tutorial.
Remove some XXX notices.
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.
