A histogram view on contributor statistics

Relevant to #2767.

```
Commits Contributors
---------------------
1       210  ....................................................................................
2        82  ................................
3        61  ........................
4        38  ...............
5        23  .........
6        20  ........
7        11  ....
8         8  ...
9         5  ..
10's     34  .............
100's     8  ...
1000's    0
```
82% of contributors are "occasional" (with <= 5 commits)

42% of contributors commit only once

43% - 54% of Casks depend on an occasional contributor

**81% - 98% of Casks depend on a contributor who is not a maintainer**