Localize loop iterators

[UnexomWid]

The loop iterators are stored in global variables. Evidently, this is bad practice. It was a temporary solution which must now be rethought. It would be better to store them in a local object, so the renderer doesn't affect the global object.

This means that the compiler needs a heuristic to determine if a token is an iterator (e.g. not a string or property of another object, not included in another token, etc). If so, it should prepend a prefix like local., which the renderer can use to refer to the local object.

[|@ item : array |] // Stays 'item'
    [|item|]        // Changes to 'local.item'
    [|"item"|]      // Stays '"item"'
[|end@|]