* Fix a bunch of issues in SPHINCS+ on Windows
* Fix testing makefile dependencies by fixing times of common files
  (affected Windows testing mainly)

* 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