Add support for `bytemuck` traits

[bradleyharden]

bytemuck seems to be the de facto standard crate for safe transmuting. Because Complex<T> is repr(C), it would satisfy the requirements for Zeroable and Pod, as long as T satisfies them as well.

Add optional implemenations of Zeroable and Pod, gated behind the bytemuck feature.

Closes #99

[bradleyharden]

@cuviper or anyone else, would you have a second to take a look at this?

[cuviper]

Can you add the feature to ci/test_full.sh? (Trivial as it is, we still ought to test it...)

[bradleyharden]

@cuviper, done

[bradleyharden]

Pinging this again. I think it's ready.

[bradleyharden]

Another bump. @cuviper?

[cuviper]

bors r+

[bors[bot]]

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