Missing generic implementation or helper

[bill-myers]

The crate seems to be missing a non-arch specific implementation, which forces anyone using gxhash to select another hash and use cfg directives to choose between them (obviously releasing non-specialized crates that only work on x86-64 and arm64 is not acceptable).

If the user selecting another hash is desired, then all GxHash types should take the other hash as a generic parameter, for user convenience.

[ogxd]

Yes you're right, it is important to provide a fallback. That's probably the 1st priority. Something can be done in the spirit of what is done for the crate ahash

[ogxd]

Closing as duplicate of #47