`nightly-float` feature for `f16` and `f128`

[tgross35]

Hello,

Rust currently has the unstable f16 and f128 types. Would it be possible to add f16_le, f16_be, f128_le, f128_be to this crate under an unstable nightly-float flag?

This should also work with bytemuck under their nightly_float flag https://github.com/Lokathor/bytemuck/blob/af8d110201aaf6e5846f146b73207f7887327638/Cargo.toml#L80-L81.