[apple movement] Apple can now move!

- When deconsructing input variables using :keys and :as you are making
  a new copy rather  than using a ref, so you cannot alter!
[snake movement] Snake now wanders randomly
[snake movement] Now wraps around

- as does apple
- need to stop snake from doubling back
[snake movement] Stopped snake from doubling back
[README.md] Added disclaimers