Cyclic Sketches

[MattyB95]

I was tasked recently with trying to find a way to allow multiple sketches to loop continuously in one graphics window. This pull request was my solution to completing that task (there was possibly a more straightforward way).

I thought I would include my work here for your consideration to move into the main project. The main files are CyclicSketch and AbstractCyclicSketch, with the remaining being examples to prove that it works as expected. It could allow others who might require something similar to be able to pick it up!

Let me know if you have any opinions either way!