Add documentation to clump breakage functions in 'bf' module
This merge request covers the changes related to preparing documentation for the 'bf' module. The following major changes are introduced:
- examples with videos,
- 'bf' module description.
Also, some minor changes:
- moved the bf module from py/bf/ to py/,
- added a minor improvement (now, before erasing the sphere all its interactions are erased as well).