Wycheproof tests vectors

[real-or-random]

Though we have good tests, the Wycheproof test vectors will be a good addition.

• The ECDSA test vectors are probably most interesting but some test vectors are incompatible with Bitcoin (see https://github.com/google/wycheproof/issues/70). We asked for other vectors there but they don't respond currently. But even if we disable the incompatible vectors (after careful checking), the other vectors will be a good addition
• Not sure if we can ECDH to work but I expect it will work at least with a custom derivation function
• SHA256 and HMAC should not be an issue

The test cases are in a simple JSON format: https://github.com/google/wycheproof/tree/master/testvectors We could either parse them (e.g., https://github.com/zserge/jsmn is very thin, MIT single-header parser that we ), or have a small script (in whatever language) that converts the vectors to C code.