Require whole number meter change offsets. In MeasureScore#to_note_score, raise error if current score is invalid.
Add support for tempo conversions
Allow single pitch to be given to Note#initialize
Make Change classes immutable and therefore non-validatable. Check for propoer tempo types depending on score type.
Add supporting methods for measure score conversion
Convert start tempo in MeasureScore#to_note_score
convert program and parts in MeasureScore#to_note_score
Add Change::Partial to deal with gradual changes that have to be divided up
Convert tempo changes in MeasureScore#to_note_score
Add testing and fix a bug for tempo change conversion
Separate measure-note-mapping function
Put tempo conversion function in the right place
roll version to 0.20.0