"schnorr" is a dirty word; the current `schnorr` module defines a
`Signature` that includes a sighash type, this sighash type is a bitcoin
specific construct related to taproot. Therefore the `Signature` is
better named `taproot::Signature`. Note also that the usage of `schnorr`
in `secp256k1` is probably justified because the
`secp256::schnorr::Signature` is just doing the crypto.
While we are at it, update docs and error messages to use "taproot"
instead of "schnorr". Also change function names and identifiers that
use "schnorr".
There is never any use for the `sighash` module unless one is signing,
which requires the `crypto` module. The `sighash` module should
therefore live in the `crypto` module. This is not an API breaking
change because we reexport it at the crate root.
Done as part of flattening util.
Currently in `util` module we have a bunch of modules that provide
cryptography related functionality.
Create a `crypto` module and move into it the following:
- ecdsa
- schnorr
- key
To improve uniformity and ergonomics, do the following re-names while we
are at it:
- EcdsaSig -> ecdsa::Signature
- SchnorrSig -> schnorr::Signature
- EcdsaSigError -> ecdsa::Error
- SchnorrSigError -> schnorr::Error
- InvalidSchnorrSigSize -> InvalidSignatureSize (this is an error enum variant)