Function parse_numeral_alone 

pub fn parse_numeral_alone(figure: &str) -> Result<NumeralAlone>

Reads the numeral off the front of a figure.

music21’s _parseRNAloneAmidstAug6, which is where the augmented sixths stop being numerals: Ger alone means Ger65, since that is the position the chord is nearly always written in, and Fr6 means Fr43 for the same reason.