base64

This adds the ability to auto-complete keys of benedicts in an interactive ipython console.
Pressing tab when entering a key of a benedict instance will offer a selection of possible keys.
This allows for quick traversing into deeper levels, when benedicts are nested.

I adapted the code from the [ipython completer in h5py](https://github.com/h5py/h5py/blob/d40791348bb54c04ab9c7e644561fc236523