Consider removing zerocopy dependency

[a1phyr]

Hi!

#162 added zerocopy dependency, which in turn brings zerocopy_derive, which brings all the proc-macro dependency. This pushes ahash very far in the compilation chain, which is damageable for such a fundamental crate.

Are you willing to revert #162, or at least to consider a cheaper alternative ?

[tkaitchuck]

Can you quantify this? From my POV,
If I just run cargo build in a clean working directory for ahash it's only building 7 things and takes about 1 sec.

[SchrodingerZhu]

@a1phyr zerocopy_derive is gated by a flag and it is not effective in ahash.

[a1phyr]

I found out that it appeared in my Cargo.lock due to the proc-macro version trick (depending on the proc-macro with a cfg(any()) target).

If no other dependency activates the feature this is fine I guess