Implement parsing for statements

[mateuszmlc]

for (let <identifier> = <expr>; <expr>; <expr>) { <statements> }

I limited the initial statement to let, which I think is the most useful one, we can add support for other statements later.

[calummoore]

Does it work without defining the let parameter? As in:

for (<identifier> = <expr>; <expr>; <expr>) { <statements> }

[mateuszmlc]

No, I'll add support for for (<let OR expr>; <expr>; <expr>) {}, which will allow that (assignments are expressions that return the value you set)

[mateuszmlc]

No, I'll add support for for (<let OR expr>; <expr>; <expr>) {}, which will allow that (assignments are expressions that return the value you set)

Added