Added support for durations

Had to make duration a double, as some chords in the data have
partial-beat durations.  Also adjusted toString methods to print the
duration in decimal form instead of character note form (w, i, etc).
Added method to calculate relative major
Renamed old Song class
Refactored to put Song into its own class
Renamed project to ThriveTones, updated README with latest timeline
Added Chord support for modes and targets

Modes currently only pay attention to the scale_degree; targets adjust
the root to be the correct scale_degree.  Further chordal modifications
have been punted to Song, as key context is required to fully identify
the chord tonality.
Bugfixes for applied targets
Improved debugability, fixed potential bug
Adjusted XMLReader for better full-data testing
Added support for 11 chords
Added support for missing keys
Merge branch 'full-data'