Python setuptools/distutils packaging

I ported the pymapnik2 packaging into mapnik.

As Python distribution is tied to mapnik release, I don't see the interest of having a separate project.

- No more manual synchronization and versioning
- Publish on PyPI as mapnik instead of mapnik2
- Works in a virtualenv

It has been tested on Ubuntu with Mapnik 2.1.0 PPA.

You just need to have libmapnik, libmapnik-dev and mapnik-utils installed.

It works the classic Python way:

- Install:

```bash
$ python setup.py install
```

- Run tests:

```bash
$ python setup.py test
```

- Make a source distribution and a binary distribution:

```bash
$ python setup.py sdist bdist
```

- Publish on PyPI

```bash
$ python setup.py sdist register upload
```

It may need a little bit of polish for Mac OSX and Windows (I can't test it).