* Add state destroy to SHA2 API
* Include optimized SPHINCS+ implementations
I've generated new implementations from the sphincsplus repository.
* Don't destroy sha256ctx after finalize
* Attempt to shut up MSVC
* Make sure to drop errors in rmtree
clang9.0.0 (https://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNotes.html)
adds a new satic analyzer: security.insecureAPI.DeprecatedOrUnsafeBufferHandling
which throws warnings if you use "unsafe" buffer handling functions which
includes memset and memcpy.
We have memset and mempy all over the place, so I think it's best to ignore this warning.
All the occurences that I looked at seemed perfectly "safe" to me.
