Metacircular interpreter's parser uses AY17/18 Source Lanugage specs

[remo5000]

Problem

• The parser that is generated using jison uses grammar that works for the previous implementation for Source
• The rules would have to be changed
  • var must be changed to const and let
  • Arrow functions must be added
  • Anonymous functions must be removed (?)

[ning-y]

Note to future devs please use functions from the actual js-slang interpreter rather than defining a separate function with separate rules (i.e. rewrite parse to use js-slang functions).

[martin-henz]

This is important for Sem 1 2019/20, not for Sem 2 2018/19.