The only reason we need `hex-conservative` is to parse strings and
format them as hex. For users that do not require this functionality we
can make the `hex-conservative` crate an optional dependency.
The `serde` feature requires `Display` so we enable `hex` from the
`serde` feature.
If `hex` feature is not enabled we still need to be able to debug so
provide `fmt::Debug` functionality by way of macros.
Close: #2654
Currently we only get `std::io::Write` impls when the `bitcoin-io`
dependency is used. This is overly restrictive, it would be nice to have
`std::io::Write` imlps even without the `bitcoin-io` dependency.
Copy the logic out of the `bitcoin_io::impl_write` macro into `hashes`
but feature gate it differently.
Call the new macro inside `hash_type` (and in `hmac`), remove the
`impls` module, and move the tests to the integration test directory.
Remove the `io` feature from `hashes`, now if users enable `std` they
get `std::io::Write` impls and if they enable `bitcoin-io` they get
`bitcoin_io::Write` impls as well.
Tobin C. Harding
Fmt Bot