Allowance

Math representation of the physically needed permissible deviation of measures in rust avoiding floating point inaccuracy.

Based of type Measure with a accuracy of 1/10th my-meter (= 0.1μ).

Exaxmple

```rust use allowance::AllowanceValue;

fn main() { let width1 = AllowanceValue::new(100.0, 0.05, -0.2); let width2 = AllowanceValue::with_sym(50.0, 0.05);

// Adding two `AllowancesValue`s is strait-forth.
assert_eq!(width1 + width2, AllowanceValue::new(150.0, 0.1, -0.25));

// `!` inverts the direction of tolerance to /subtract/ measures.
assert_eq!(!width1, AllowanceValue::new(-100.0, 0.2, -0.05));

// Adding an inverted `AllowanceValue` wides the tolerance.
assert_eq!(width1 + !width1, AllowanceValue::new(0.0, 0.25, -0.25));

} ```