ES6 Support

[TopchetoEU]

Currently, the engine has good ES5 support. However, for any real-world application having ES6 support is imperative.

The following features ought to be implemented:

• Arrow functions (ES6 Support Groundwork + Fixes #26)
• Default arguments (ES6 Support Groundwork + Fixes #26)
• Spread arguments (ES6 Support Groundwork + Fixes #26)
• ES6-style variable declarations (let and const) (ES6 Support Groundwork + Fixes #26)
• Variable, parameter and assignment deconstructions (ES6 Object and assignment destructors + object stuff #28)
• Object literal shorthands, methods and computed keys (ES6 Object and assignment destructors + object stuff #28)
• Class definitions (Classes #29 WIP)
• Array deconstructors
• Spread syntax in objects
• Spread syntax in arrays
• Spread syntax in calls (and dynamic argument count in calls)
• Nullish coalescing operator and assignment (??)
• Optional indexing (.?)
• &&= and ||= operators (ES5 features that are missing)
• Generator functions
• new.target
• Exponent operator
• For-of loop
• Optional parsing mode for ES module files

The following will NOT be implemented:

• eval() - brings multiple complexities into the project, mostly with the resolution of variables in the runtime, for the benefit of a feature which is unsafe and has the better alternative of the Function constructor
• Non-strict context (aka JS code will be compiled and run "use strict" implied)