Add version pinning to all dependencies (thanks @dbrgn) and various little tweaks to setup.py ported from saltyrtc.server
Add version pinning to all dependencies (thanks @dbrgn) and various little tweaks to setup.py ported from saltyrtc.server

Closes #28

threema-ch/threema-msgapi-sdk-python,lgrahl/threema-msgapi-sdk-python