Adds rand_distr::Distribution implementations for f16 & bf16

[coreylowman]

Resolves #82

Tests need to be run with the sample and num-traits feature enabled

[coreylowman]

Happy to make any modifications you'd like to any names!

[starkat99]

I'll happily merge this with the following changes:

• Could you rename the feature to simply rand_distr to match the name of the optional dependency. Since it's just implementing traits from the crate and not adding any additional functionality, this makes the feature the most clear, matching the other optional crate trait implementations.
• Could you add the new rand_distr feature to CARGO_MAKE_CARGO_ALL_FEATURES in Makefile.toml so the tests get run in CI? That way the tests can run before I merge.
• I didn't see anything relying on num-traits in the tests, but if they do rely on that dependency like you said, could you put a #[cfg] on the tests so they don't break compiles if tests are run with rand_distr but without num-traits?
• Could you also add a brief note in the Readme and crate docs (in lib.rs) documenting the optional cargo feature? There's a section in both docs for optional cargo features. Saves me from having to write it, especially since I've never used rand_distr before.

That's it, just minor things other than the rename.

[starkat99]

Oh also, it doesn't look like rand crate is actually used outside of tests, so it doesn't need to be a regular dependency, just a dev-dependency. And add the feature to the [package.metadata.docs.rs] section so trait implementations will appear on docs.rs

[coreylowman]

Perfect, will make those updates soon! Thanks for the response 🚀

[coreylowman]

Also for completeness, here's the errors you'll get if you run the tests without num-traits:

error[E0277]: the trait bound `binary16::f16: Float` is not satisfied
   --> src\rand_distr.rs:103:13
    |
102 |         let _: crate::f16 = rng.sample(
    |                                 ------ required by a bound introduced by this call
103 |             rand_distr::Normal::new(crate::f16::from_f32(0.0), crate::f16::from_f32(1.0)).unwrap(),
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Float` is not implemented for `binary16::f16`
    |
    = help: the following other types implement trait `Float`:
              f32
              f64
    = note: required for `rand_distr::Normal<binary16::f16>` to implement `Distribution<binary16::f16>`
note: required by a bound in `rand::Rng::sample`
   --> C:\Users\clowm\.cargo\registry\src\github.com-1ecc6299db9ec823\rand-0.8.5\src\rng.rs:152:21
    |
152 |     fn sample<T, D: Distribution<T>>(&mut self, distr: D) -> T {
    |                     ^^^^^^^^^^^^^^^ required by this bound in `rand::Rng::sample

[coreylowman]

The rand::Rng trait is used in this impl Distribution here. Unfortunately rand_distr doesn't re-export Rng, so thats the only use of it.

This would mean users would always have to use --features rand,rand_distr together. Thoughts?

[coreylowman]

Just kidding I think I figured out how to do this by adding an actual feature named rand_distr that requires both rand & rand_distr

[coreylowman]

Okay should be all good for re-review!

[coreylowman]

@starkat99 anything else I need to update?