Pbxplore

- add some unit tests
- add a function test() within the root path of PBxplore
- add a Release file
- Use of bumpversion to sync version across files
- Add MDAnalysis as a mandatory module
- Add matplotlib as a mandatory module
- Fix weblogo weblogolib.SymbolColor/ColorGroup import
- Remove R clustering (now in branch clust_R)

- remove pbxplore import from setup.py and add version number

- remove --flat and --phipsi from PBassign (and related functions in the api)
- improve documentation to produce results similar to what --flat and --phipsi options used to produced
- many performance improvements in the assignment of PBs

- PBxplore is installable via pypi
- api documentation
- PBXplore is installable with setup.py