Log Message:
Update to 0.60

Changes:
- Again some code cleanup and bug fixes.
- The configuration file layout has changed a little bit: You might have to
  check your settings in the GUI and to save the new configuration again.
- Window/fullscreen mode is now correctly initialized from the configuration
  file.
- Added --window command line option to force a start in window mode.
- Added alert boxes to show warnings, errors and information messages.
- PC mouse pointer is now better in sync with the ST mouse pointer.
- It's now possible to load an alternative cartridge image file.