Modus cum tempore

[goursaud]

We need support for modus-cum-tempore mensuration signatures within {mens}, e.g. {mens: O2}, {mens: C3}, etc. We need to be able to specify the vertical position on the stave as normal, by following the mensuration symbol with a numerical value, so a code symbol may need to be established to represent O2 in order to avoid syntax problems.

[goursaud]

We also need to be able to encode modus-cum-tempore mensuration signatures where the numeral is placed directly below the modus sign rather than to its right.