Add .gitignore

For ignoring files that don't belong in source control
Use absolute paths.

This ensures 2 things:
- pydown can be used outside of the project directory
- pydown can be crossplatform
PyPI ready

- Adds setup.py with pydown entry-point
- Adds MANIFEST.in
- Adds NOTICE
Merge pull request #9 from sloria/pypi

PyPI ready!