Convert numerics to mixed_num / NDSP

[timschmidt]

Dependency chain looks like this:

https://docs.rs/fixed/1.29.0/fixed/
https://docs.rs/fixed_trigonometry/latest/fixed_trigonometry
https://docs.rs/mixed-num/0.5.5/mixed_num/
https://docs.rs/ndsp/latest/ndsp/

NDSP provides functions over Vecs of mixed-num and may be useful.