Misc improvments

[Sajjon]

• [x] Add link to documentation in README, solved in #32
• [ ] Clean up test folder structure, names etc
• [ ] Upgrade Wycheproof testvectors to v1
• [x] Serialization/deserialization roundtrip tests for ALL inits/serialize of ALL PublicKeys, fixed in #33
• [ ] Serialization/deserialization roundtrip tests for ALL inits/serialize of ALL PrivateKeys
• [ ] Add soundness.sh script see swift-crypto
• [ ] Add API breakage check as part of CI, see swift-crypto
• [ ] Move ASN1Error into K1.Error (hiding it from top level documentation)
• [ ] Integrate Compact into ECDSA.NonRecoverable/ECDSA.KeyRecovery so that the entire API of ECDSA.NonRecoverable/ECDSA.KeyRecovery becomes that of Compact (and make Compact "invisible" (internal))