Macro ValueUnit

macro_rules! ValueUnit {
    ($value:literal $($unit:ident$(^$power:literal)?)*) => { ... };
}

Allways use this macro to create a ValueUnit
Use in the following way:

use value_unit::*;
let g = ValueUnit!(9.81 m s^-2);
let t = ValueUnit!(100 s);
assert_eq!(g * t, ValueUnit!(981 m s^-1));

Units can be anything:

use value_unit::*;
let price = ValueUnit!(10.99 euro pizza^-1);
let amount = ValueUnit!(100 pizza);
assert_eq!(price * amount, ValueUnit!(1099 euro));