Move sub and sub-subtest documentation into their modules

Putting the docs. next to the code solves multiple problems:

*  Un-clutter main documentation
*  Help keep docs current by closer proximity to likely areas of change
*  Provide reporting-accessable human-readable description mapping to test names.
*  Allow for easier verification of general formatting in Travis CI.
You're right, my only fear is by not having it, it's easier to forget to update it :)  Do you think this is maybe not a true problem though?