Add a link, so the warning will now link to rails-bestpractices.com

This link provides a description and a solution to the problem.
Call RailsBestPractices directly to get access to the array of errors.

We now have the URL, so we can provide a link to rails-best-pracitces.com
By calling the lib directly we can avoid IO overhead, however we want to
be sure that the RailsBestPractices maintains the interface we are
expecting, since it's not a publicly advertised interface.
I have added some specs that will error if the interface to
RailsBestPractices changes.

huh
Update History
Merge branch 'rails-best-link-to-warning' of https://github.com/calveto/metric_fu into calveto-rails-best-link-to-warning

Conflicts:
	HISTORY.md
Remove no-longer-necessary rbp executable
BF Merge branch 'calveto-rails-best-link-to-warning'