Incorporate fractions table

[curran]

We need to incorporate the following table into mensurations.csv.

Mensuration,Relative duration of one measure
O,1
Cut-C,1/2
Cut-C3,1/2
3,1/2
O-over-3,1/2
Cut-O,3/4
C3,1
C-Dot,1
O2,1/2
reverse-C,1/4
Cut-C2,1/4

[curran]

Part of #12