Add Python binding

I've added a Python binding to HashPump, so that it can be used directly.

It is available [on PyPI](https://pypi.python.org/pypi/hashpumpy/1.0) and can be installed via `$ pip install hashpumpy`.

Here's an example:

```shell
user@ubuntu:~$ pip install hashpumpy
Downloading/unpacking hashpumpy
...
Successfully installed hashpumpy
Cleaning up...
```
```python
>>> import hashpumpy
>>> hashpumpy.hashpump('ffffffff', 'original_data', 'data_to_add', len('KEYKEYKEY'))
('e3c4a05f', 'original_datadata_to_add')
```
```shell
$ hashpump --signature ffffffff --data original_data --additional data_to_add --keylength 9
e3c4a05f
original_datadata_to_add
```