Add class for playing music.
Build main window with sdl.png.h.
PNG data to display the SDL logo.
Move member "id" to protected.
Clean doxygen generated files.
Add svn:ignore property for "doxygen".
Add documentation.
Add rule to make "docs" for creating doxygen documentation.
Add "doc" folder for documentation.
Add Doxyfile for creating documentation with doxygen.
