Environment Aware Codegen

[gaurangsadekar]

Almost completely rewrote codegen. It now generates code using a little more scope information, as opposed to the word for word translation we were doing initially.

Did this because of Javascript's funny behavior with 'let' and 'var' scoping. New codegen enforces more traditional scoping and shadowing rules in local and global scopes.

Fixes #72

[bahuljain]

jaldi kar, warna mein merge kar dunga!!!

[prakhar1989]

Sex work, guys!!! 👯