Add a script that prints monthly lines added/deleted

Script currently prints:
```
Cumulative unique author count (since open sourcing)
2014-03-10..2014-04-10, 11
2014-03-10..2014-05-10, 17
2014-03-10..2014-06-10, 23
2014-03-10..2014-07-10, 24
2014-03-10..2014-08-10, 28
2014-03-10..2014-09-10, 30
2014-03-10..2014-10-10, 30
2014-03-10..2014-11-10, 31
2014-03-10..2014-12-10, 35

Lines of *.[Ch] files added/deleted:
2014-03-10..2014-04-10, +5277, -2105
2014-04-10..2014-05-10, +14488, -5982
2014-05-10..2014-06-10, +19025, -5778
2014-06-10..2014-07-10, +6390, -3711
2014-07-10..2014-08-10, +8146, -2248
2014-08-10..2014-09-10, +8629, -1936
2014-09-10..2014-10-10, +7457, -3405
2014-10-10..2014-11-10, +3274, -2208
2014-11-10..2014-12-10, +10295, -3927

Lines of *.py files added/deleted:
2014-03-10..2014-04-10, +461, -270
2014-04-10..2014-05-10, +99, -75
2014-05-10..2014-06-10, +6274, -390
2014-06-10..2014-07-10, +186, -35
2014-07-10..2014-08-10, +129, -46
2014-08-10..2014-09-10, +76, -37
2014-09-10..2014-10-10, +7215, -7196
2014-10-10..2014-11-10, +378, -236
2014-11-10..2014-12-10, +2408, -383
```