Some majors finalization for OGAM submission

* Added config file 
* Set screen to 800x640
* Set size of snake/food to 16x16 for each block
* Added credits on main screen
* Added sound on/off switch with S key
* Added sounds for die,food,start,bum
* Added control limitations for opposite ways

*Observation: The game still needs some polishing 
to be a good simple classic