Parser / AST Implementation

[dineshUmasankar]

Implement the Parser by completing Chapter 2 of Thorsten Ball's Monkey Language
Pages 29-102

These implementations will be split up into several smaller PRs where each member will take upon themselves an implementation of each subchapter (2.1 to 2.9).

• Chapters 2.1 - 2.4 (Parse Let Statements) #14
• Chapter 2.5 (Parse Return Statements) #20
• Chapter 2.6 - 2.8 (Parsing Expressions) #22
• Chapter 2.9 (REPL) #34