Fractional sharp notation

VERY WIP (I'll move it to the main namespace if it's finished.)

The letter notation is a notation scheme developed by CompactStar for just intonation up to the 29-limit and some equal and multirank temperaments. It is Pythagorean notation with the letters H-Y used as accidentals for higher prime limits (starting from H to avoid confusion with note names).

Accidentals

Prime limit	Letter	Ratio	Letter	Ratio
5	H	81/80	I	80/81

For example, 5/4 is IM3 (I-major third) and 7/4 is Km7 (K-minor seventh).