switch to absolute imports
Do not install itself in requirements, this drove my pip nuts
Support absolute templates path
Add a default __main__.py to make "python -m staticjinja" possible

This way the most simple behavior can be triggered without a build.py at all:
simply run `python -m staticjinja` and templates in ./templates get built
to . with debug=True and use_reloader=True
Merge pull request #14 from FiloSottile/shortcut

Shortcut for default behavior, and bonus