Triangle facts 20140929 rc

Mostly coding style updates, based on the following docs:
https://github.com/thoughtbot/guides/tree/master/style#ruby
https://github.com/styleguide/ruby

Some refactoring, notably:
-removal of specific triangle type functions, in favor of one method that returns the type
-addition of third test case, now covers all triangle types
-addition of `angles` variable, cleanup/readability changes to `calculate_angles`
Yeah, prefer underscored variables to mixed case. So, angleA should be angle_a.

There's a deeper problem though, which is the naming. angle_a implies a relation to a, & yet that's left implicit. I would suggest either use a different naming convention (angle_x, angle_y, angle_z) or add a comment to make the relationship clear.