Move docs from Django to website

[JasonGrace2282]

Since we have our website there's really no reason to host docs on Tin itself anymore.
I did try to improve the docs wherever possible, especially by adding more examples of graders.

TODO

• remove docs from Django
• organize the docs in the sphinx builds
• add more examples for graders
  • Fibonacci example
  • File IO
  • an example with autorunning submissions with a specifically named function