Added a simple stack library for function calls and other uses, along with some smaller graphics programs such as screen/rectangle_fill.craw

This is also my official announcement that I’ll be doing much less programming, due to summer holiday starting now. This is because I can’t program during family time, camping weeks, and other events. In addition, I have University after summer holidays, so this reduced productivity will continue throughout the rest of Stardance. Thank you all for making Crawssembly the number 1 project on stardance!