Add `encase` trait implementations

[teoxoy]

I would like to remove trait implementations on foreign types from encase for the reasons listed in teoxoy/encase#94.

They are currently hosted here: https://github.com/teoxoy/encase/blob/fcc83d706f4a51bfbe22c9901973f1c2fa806526/src/impls/cgmath.rs

Before releasing a v0.12 with all optional features removed, I would like to first get a confirmation that cgmath developers are willing to host the trait implementations.