Currently we have a trait `Hash` that is required for `Hmac`, `Hkdf`,
and other use cases. However, it is unegonomic for users who just want
to do a simple hash to have to import the trait.
Add inherent functions to all hash types including those created with
the new wrapper type macros.
This patch introduces some duplicate code but we are trying to make
progress in the hashes API re-write. We can come back and de-dublicate
later.
Includes making `to_byte_array`,`from_byte_array`, `as_byte_array`, and
`all_zeros` const where easily possible.
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