Convenience functions, Python3/doc fixes

• Add tutorial 7d7ea0a
• Add support for sustain pedal in piano roll e3ab5f9
• get_duration and duration property for Note objects 9851c0c
• Fix get_beats for compound meters 369ce98
• Enforce strictly increasing times in adjust_times bd97acd
• Update librosa calls in example 6e767d3
• Bugfixes, docfixes, and Python3 compatibility 3a9153f 4fa04b0 2008db6 d13d78b 48fae35 78e33ab 82083e0