Figure out docs generation for only changed files since previous day

[vsoch]

Right now we try to regenerate everything - and while that is okay, likely we want a way to only regenerate those that are actually changed! Another script could help here - maybe a Python wrapper that starts with an shpc show to get all modules, but then adds in git history to find just changed files in the last 2 days.

[vsoch]

This isn't huge priority, but it might look like this:

1. clone the repository
2. use git to get changed files in last two days eg here
3. run a python script that uses shpc directly to run docgen on only those that are changed (and removes them before generating again)

Note that these scripts live in the gh-pages branch.