Create rotatable classes

I'm coming from FontAwesome where there are utility classes for rotating icons, as well as stacking, and animating.

Would it be possible to add some of this functionality? Partly this comes from the same problem as https://github.com/google/material-design-icons/issues/71.

Being able to rotate the `.mdi-action-exit-to-app` icon 180º would solve that.
(love the icons btw. really great)

The issue names no files, tests, or entry points. First clarify whether rotation, stacking, and animation are all in scope; done would mean an agreed utility-class design that supports rotating the exit-to-app icon 180º and covers the requested functionality.

Written by the indexing model from the issue text.