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`