Level select and buttons

After some feedback, I've improved a couple of things that were pointed out to make things a bit easier and more fun. 

• Firstly, it can be quite the marathon run to get through it from start to finish so I've added check points at every five levels. These can be accessed from the new level select button on the main menu.
• In addition, I've added keyboard buttons to activate the color buttons on screen. Using 1 or J activates red, 2 or K activates green, and 3 or L activates blue. In the future I will make them mappable to a key of the player's choosing. 

I greatly appreciate everyone who took the time to give a chance, and to those who offered suggestions and feedback.