Working setup.py using vcversioner

The `setup.py` file now works. It uses [vcversioner](https://pypi.python.org/pypi/vcversioner) to extract the current version from the latest properly-formatted git tag (either `1.0` or `v1.0` format). It is configured to create the file `i2p/i2cp/_version.py` with the discovered version information, which will be included in the built egg and added to the module per [PEP 396](http://legacy.python.org/dev/peps/pep-0396/).

Until the first version is tagged, you can use the `setup.py` file by creating a `version.txt` file in the base directory containing `0.0-0-00000000` (a fake version).