file organisation + setup refactoring: - `/src` has been renamed to `/sat_pubsub`, this is the recommended naming convention - revamped `setup.py` on the basis of SàT's `setup.py` - added a `VERSION` which is the unique place where version number will now be set - use same trick as in SàT to specify dev version (`D` at the end) - use setuptools_scm to retrieve Mercurial hash when in dev version