Added file to store prototyping work with SDL_ShowMessageBox
#70 Prototyping gui Button

Added a prototype Button class
Added a MouseMoveCommand
Extended InputService to handle mouse motion events #68
#70 Added some description of basic gui design
Closes #65  Added a PlayMusicCommand class

Added a command to play a music resource based on a specified id
"Closes #66"  Added a command to play sound effects
Merge branch 'dev-commands' into dev
Merge branch 'dev'