removed BPMRubato from RhythmExtractor, RhythmExtractor2013, RhythmDescriptors algos, example extractors and tests

BPMRubato algorithm is not reliable and performs poorly.
- add note that BPMRubato works poor to doc
- add note that RhythmExtractor is outdated to doc
- commented related code for running BPMRubato within rhythm-related algorithms
- commented/fixed related code in extractors and tests