[BugFix] AST construction error: Remove unsupported comma

[BugFix] to_string() not in scope: Enable c++11 support

Update project documentation and example

Rename BNF file; Update Make instructions

Update project documentation and example

Rename template directory to input (relevant)

Restructure Project's test files and directories

Restructure Project's source directories

[BugFix] Syntax errors in code generation

Add builtins.cpp and tests for code generator

Modify main program to include the code generator

Fix checker import error on various consts and functions

Function calls and infix expressions

Generate integers, bools and strings

Generate if statement and custom function body