`Val::frac` for fractional value units

## What problem does this solve or what need does it fill?

`Val::Percent` exists, but it's on a scale of `0.0 - 100.0` which feels unnatural considering fractional values are typically from `0.0 - 1.0`. But this makes sense, since it's a *percentage*. This proposes a helper function on Val, `pub fn frac(f: f32) -> Val`, making a `Val::Percent`.

## What solution would you like?

```rs
impl Val {
pub fn frac(f: f32) -> Self {
Self::Percent(f * 100.0)
}
}
```

## What alternative(s) have you considered?

- Just using `Percent` but again this feels unnatural

- Implementing that helper function myself:

```rs
pub trait ValFrac {
fn frac(f: f32) -> Self;
}

impl ValFrac for Val {
fn frac(f: f32) -> Self {
Self::Percent(f * 100.0)
}
}
```

## Additional context