Add correct implementations of merge/groupBy to Analysis.

Copious comments to explain the non-trivial logic.
Update home.rst

It took me a while to find where the documentation was in the GitHub repository.  Maybe pages could link back to their source?
Complete code example in Custom-Settings.rst

The original wording confused me.  I thought it meant that there was no point to my new keys unless I used them in a task.  But rather it meant that I needed to create keys for my task and then a task definition with the same key name.  I added the creation of the keys to the task implementation code example to clear this up in the future.
Merge remote-tracking branch 'benjy/analysis2' into 0.13