Add adaptive tuning

[Woyten]

Retune played notes in real time s.t. their frequency ratios get as close to JI as possible.

Usage: The user provides a list of (pure) intervals some of which can be left empty.

Example: x, 9/8, 6/5, ... means minor seconds have no preference, major seconds prefer to become 9/8, minor seconds prefer to become 6/5, etc.

Idea: Optimize two energies

• The sum over all intervals of the squared difference between the actual interval and the just interval
• The sum over all pitches of the squared difference between the actual pitch and the original pitch

Enhancements: Provide a weight for each ratio.