Macro pop_ret

macro_rules! pop_ret {
    ($interp:expr, $x1:ident, $ret:expr) => { ... };
    ($interp:expr, $x1:ident, $x2:ident, $ret:expr) => { ... };
    ($interp:expr, $x1:ident, $x2:ident, $x3:ident, $ret:expr) => { ... };
    ($interp:expr, $x1:ident, $x2:ident, $x3:ident, $x4:ident, $ret:expr) => { ... };
    ($interp:expr, $x1:ident, $x2:ident, $x3:ident, $x4:ident, $x5:ident, $ret:expr) => { ... };
}

Pops U256 values from the stack, and returns ret. Fails the instruction if the stack is too small.