Alpha 0.2

+ Added shop button.
    * Currently does nothing, it's just for testing.
    * Appears when the player has 100 or more coins.
    * Increased coin income to 100 per second for testing purposes.

* Changed look of buttons completely.
    + Buttons now react to being pressed.
    - Text on buttons can no longer be selected, because it was
annoying.

* Cleaned the stylesheet up.
    + Different appearances of buttons (normal and pressed) are kept as
seperate classes, for much easier management.
    * The position of everything on screen is now classified as
"absolute", for easier management.

+ Added a note about "Alpha."