consistent whitespace & PEP8 compliance

Some un-[PEP8][pep8]tish code slipped into the code.

Internally we check for such tings automatically and rigurously to minimize whitespace changes and other stuff which otherwises clutters our change sets and makes merging more difficult than it should be.

This patch addresses concerns of:

    $ pyflakes nbt examples tests
    $ pep8 -r --ignore=E501,W191,E101 nbt examples tests

It also adds a simple makefile to allow easy checking. Just type `make`.

[pep8]: http://www.python.org/dev/peps/pep-0008/