Currently we have an implementation of `Debug` (also used by `Display`)
for `Signature` that first converts the sig to a `SerializedSignature`
then prints it as hex.
We would like to have an implementation of `Debug` for
`SerializedSignature`, this cannot be derived because of the `data: [u8;
field]`. We can manually implement `Debug` for `SerializedSignature`
exactly as it is currently done for `Signature` and call this new
implementation from `Signature::fmt()`.
This code path is already tested in `lib.rs` in the test function
`signature_display`.
This documents the Cargo features making sure docs.rs shows warning for
feature-gated items. They are also explicitly spelled out in the crate
documentation.
With the introduction of Schnorr signatures, exporting a `Signature`
type without any further qualification is ambiguous. To minimize the
ambiguity, the `ecdsa` module is public which should encourage users
to refer to its types as `ecdsa::Signature` and `ecdsa::SerializedSignature`.
To reduce ambiguity in the APIs on `Secp256k1`, we deprecate several
fucntions and introduce new variants that explicitly mention the use of
the ECDSA signature algorithm.
Due to the move of `Signature` and `SerializedSignature` to a new module,
this patch is a breaking change. The impact is minimal though and fixing the
compile errors encourages a qualified naming of the type.