Allegro platform

* Added an Allegro 5.1 platform to Gwen to support OSX.
* Designer working on Mac. Various fixes for Allegro Gwen renderer.
* Replaced space indents with tabs due to conflicting editor settings.

Sorry, I should have created these features in a branch. I think that would have made these pulls easier? I'm new to Github and whatever the preferred workflow is.

I'd quite like to the designer up and going. I use Mac at home and Windows at work. I guess an advantage of having an Allegro platform is that it supports all platforms that Allegro supports. However, some features are currently lacking in Allegro, e.g. Window manipulation to do full platform implementation.

For the designer I think I'd like to have some sort of adapter, which could glue the game code and UI together.