Function mksvg::write::qcast

pub fn qcast<A: CDNum, B: CDNum>(a: A) -> B

qcast (quick cast) is makes it simple to use primitives with an unknown CDNum type

use mksvg::write::{qcast,CDNum};
fn f<T:CDNum>(n:T)->T{ n + qcast(20)}
assert_eq!(f(1.0),21.0);
assert_eq!(f(1),21);