structured slugs compiler

Turns the python sources for the structured slugs -> slugsin compiler into a `python` package called `slugs`, for easy installation. Main other changes:

- allow parsing a `str` and returning (instead of printing) a `str`, in addition to command line usage
- rename function for parsing a structured slugs `str` to `slugs.compiler.convert_to_slugsin`
- do not maintain global state in the parser, because it causes errors when the same parser instance is reused (typical when the package is imported). Add example demonstrating the bug
- [use `logging`](https://docs.python.org/2/library/logging.html#) from the standard library, instead of `print`
- [use environment `python`](http://stackoverflow.com/questions/2429511/why-do-people-write-usr-bin-env-python-on-the-first-line-of-a-python-script), instead of `/usr/bin/python` (e.g., `virtualenv`, macports, etc.)
- use [`autopep8`](https://pypi.python.org/pypi/autopep8/1.0.4) to increase readability and apply [PEP8](https://www.python.org/dev/peps/pep-0008/) conventions.

Some misc files have been added to `.gitignore`.

The `pep8` formatting was mainly automatic and is thus not the best, but it is a starting point that can be edited further.