Implement fractions in time spines

[craigsapp]

Such as:

**dtime	**ratio
*	*Iflt
*	*ref:A3
1/2	1
1/2	2
1/4	1
1/4	2
1/8	1
3/8	2
1/12	1
1/12	2
1/12	1
1/12	2
1/12	1
1/12	2
1	1
*-	*-

(currently only the first number in the fraction is read for the time value).

[craigsapp]

Mixed fraction version:

**time	**ratio
*	*Iflt
*	*ref:A3
0	1
1/2	2
1	1
1+1/4	2
1+1/2	1
1+5/8	2
1+6/8	1
2	2
2+1/12	1
2+2/12	2
2+3/12	1
2+4/12	2
2+5/12	1
*-	*-