We are about to release `bitcoin_hashes 0.15.0`, replace the TBD string
with the version number.
Requires changing `allow(deprecated_in_future)` attribute to
`allow(deprecated)` (in functions that are them self deprecated).
We have two files one for public macros and one for private macros. Move
the `engine_input_impl` macro to the private macros file.
Requires change to call sites because we do not have `use_macros`
attribute on the `internal_macros` file.
These three macros are solely provided to reduce code duplication, they
are only part of the public API because they are used by the "real"
public macro `hash_newtype`.
Roll the `serde_macros` module into `macros`, requires making `macros`
public but since it explicitly holds public macros this is reasonable.
Keep the original module and deprecate it.
Tobin C. Harding