Scrypt - let expressions

[kroezone]

Scrypt should probably have a statement equivalent to the usual (let [...] ....) form in Lisp

Examples:

let (x=1) x+2;
let (a=1, b=a+1) {a * b;};
(1 + let (b=10) b*b)

Might need to think a bit about whether semicolons are mandatory. Probably not? We should perhaps think of this as a let expression rather than a statement?