More test signatures

[wqweto]

You can check out ecdsa_test.json from wycheproof test vectors they have vectors for sec256k1 signatures too, among many other curves.

For instance your EcdsaSig.parse method does not understand "long form encoding of length of sequence" so it will fail on some of the test cases from the wycheproof repo.

[bmancini55]

Ah very good info, thank you!