Merge pull request #52 from hector/2.0

Add peak interpolation to PitchYinFFT algorithm
fixed allowed interval for magnitudeThreshold param in SpectralPeaks

It was impossible to setup a threshold for values on db scale as they were negative.
Merge branch '2.0' of https://github.com/MTG/essentia into 2.0
update documentation for SpectralPeaks
Added function that tries to fix and strips invalid UTF8 characters when reading tags in MetadataReader
Fix typo in extractor's command-line help text
update documentation with info about high-level models
Merge branch '2.0' of github.com:hector/essentia into 2.0

Conflicts:
	doc/sphinxdoc/algorithms_overview.rst