In this commit, we add a new function `RawTxInTapscriptSignature` that
will be used to generate signatures in the _tapscript_ context. Note
that this differs from top-level taproot as a distinct sighash is used,
and we _always_ accept a root hash to perform the proper tweak.
This was the version tagged that created the new `ecdsa` and `schnorr`
packages. Updating these pinned version lets importers properly use
these packages and build. Things build as is since we use replace
directive to point to the latest version _in the repo_ when we build.
In this commit, we add an initial implementation of BIP-340. Mirroring
the recently added `ecsda` package, we create a new `schnorr` package
with a unique `Signature` type and `ParsePubkey` function. The new
`Signature` type implements the fixed-sized 64-byte signatures, and the
`ParsePubkey` method only accepts pubkeys that are 32-bytes in length,
with an implicit sign byte.
The signing implementation by default, deviates from BIP-340 as it opts
to use rfc6979 deterministic signatures by default, which means callers
don't need to always pass in their own `auxNonce` randomness. A set of
functional arguments allows callers to pass in their own value, which is
the way all the included test vectors function.
The other optional functional argument added is the `FastSign` option
that allows callers to skip the final step of verifying each signature
they generate.
In this commit, we create a new package to house the ECDSA-specific
logic in the new `btcec/v2` pacakge. Thsi c hange is meant to mirror the
structure of the `dcrec` package, as we'll soon slot in our own custom
BIP-340 implementation.
Now that the new `btcutil/v1.0.0` tag has been pushed, we update the new
internal modules to point to the top-level `btcd` repo via replace
directives.
In this commit, we update all the btcutil imports to point to the new
sub-module.
In the same commit, we also modify the recently added `btcutil/go.mod`
file as we need to continue pointing to the _old_ version of btcd, until
we merge this PR and push a new tag.
