fixes #14
Merge pull request #16 from IagoLast/iss14

fixes #14
Lots of changes:
Created Widget and ImageButton classes.
Changed directory structure.
Added Constants.py to hold constants.
Fixed image loading method to support images with alpha channel
Changed Layer and Scene concept: A Scene is everything you see on the screen, which is composed of layers.
Created Main menu.
Create README.md
Create .gitignore
Removed *.pyc
Fixed some bugs
Updated maps too
Added some sprites. Feel free to add moar.
Merge pull request #17 from dgalaktionov/master

Added some sprites. Feel free to add moar.
Added new tiles, maps folder refactor.