jamescgibson and trevnorris Add missing calculation of adjusted R^2
The Ordinary Least Squares module was not computing the adjusted R^2

Resolve this issue, additionally adding a test for the correct
calculation, and further document the test, code, and generated
documentation to clarify for users which adjusted R^2 value is being

Thank you to EloquentData for reporting the issue.

Fixes: #219
PR-URL: https://github.com/jamescgibson/jstat/pull/221
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
Latest commit c306885 Sep 28, 2017