BLD: Use versioneer to handle version numbers

Rebase of @leouieda #128 onto v0.2.2. It works:

```
python
>>> import trackpy
>>> trackpy.__version__
'0.2.2-6-ge1a6913'

git tag v0.2.3rc1

python
>>> import trackpy
>>> trackpy.__version__
'0.2.3rc1'
```