Add modulo to Row struct, allowing rows to have a modulo value other …

[mikowitz]

…than 12

Webern.row([0, 1, 2, 3, 4, 5], modulo: 9) is now valid syntax.

The modulo of a row is based on either the value passed in to the keyword list, or the highest value in the row itself. When the modulo argument is not present, it will be set to the highest value in the row + 1. This works best with integral-based rows. Rows using non-integral values (quarter tones, Hz, or other non-dodecaphonic scales) should specify their modulo to avoid unexpected transformations.

New usage:

Webern.row([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]) #=> modulo 12 (11 + 1)
Webern.row([0, 1, 2, 3, 4, 5]) #=> modulo 6 (5 + 1)
Webern.row([0, 1, 2, 3, 4, 5], modulo: 7) #=> modulo 7