Using the notation data packets of signatures, we add a way to
set a context to detached signatures.
We also add a way to enforce that signatures have the right context
during verification.
Instead of parsing the signature packets manually, use the signature
packet returned by VerifyDetachedSignatureAndHash to get the
signature creation time.
* Reduce complexity of SignatureCollector.Accept
* Add stylecheck linter, and lint accordingly
* Rephrase some comments
* godot - Top level comments should end with a dot.
* nestif - Reduce nested complexity of code
* Review changes
Co-authored-by: Aron Wussler <aron@wussler.it>
