fixed broken doxygen documentation
more updates to documentation
small fixed to the algorithms' description
moved beatogram related python scripts to examples/python/experimental
better simpler naming for extractors, moved some old extractors to examples/outdated
fixed spectral contrast extractor (removed pca, output both coeffs and valleys separately)
fixed empty output in tuning frequency extractor
removed a dummy extractor which was possibly used to test scheduler refactoring and is not required anymore