Variables are marked as defined before initialization

[Bigjango13]

When let foo is parsed, foo is added to parser.ast.vars so it can be used in the future, this works for functions (as they can be recursive), but it doesn't for variables. The easiest way to reproduce this is burlap - 'let x=x;' which outputs:

Runtime Error at <cli>:1: no variable called "<cli>::x"! This is a bug in burlap and should have been detected earlier on