Updates to: Promises, Iterables, Arrays, and syntax.
+ Added first pass at `setTimeout` (still needs to be cancellable)
Syntax highlights:
+ nil coalescing operator `??`
+ added nilable modifier to coercives (e.g. `function?`)
+ shortcut for #{} and #[] forms (performance)
+ added `static` as a modifier to properties in object literal (still unsure whether this is a good idea)
+ trailing comma in array literal means nil
+ trailing comma in object literal not allowed