bfi - brainfuck interpreter/jit

TODO:

• interpret AST at runtime
• optimise the AST (http://calmerthanyouare.org/2015/01/07/optimizing-brainfuck.html)
  • clear loops
  • simplification (+x5 -x3 == +x2)
  • copy loops
  • multiplication loops
  • scan loops
  • operation offsets

pros:

• simple
• has an AST for expandability

cons:

• naive
• minimal optimisations
• memory hungry due to AST