mirdata v.0.3.0

First mirdata realese of the 0.3 series. Main changes included in the release are:

New Loaders

• AcousticBrainz Genre
• cante100
• IRMAS
• Saraga Carnatic
• Saraga Hindustani
• Tonality classicalDB

Features

• Changes top level API - datasets are now loaded with mirdata.initialize('orchset')
• Adds a Dataset object
• Renames load --> load_tracks
• Adds dataset.choice_track()
• Moves Track and MultiTrack base classes from mirdata.track to mirdata.core
• Extends index structure beyond tracks and adds version as mandatory top-level key
• Introduces of datasets submodule
• Introduces of Annotation classes for different time-series data types
• Improve documentation
• Introduces support for remote indexes for big datasets
• Specify license in each dataset
• Config flags for automatic full-dataset testing each week 

And bug fixes. See details in here.