Add fully specified algorithms

[kentakayama]

Resolve #224 based on the Option A.

Key modifications are:

• AlgorithmESP256, AlgorithmESP384, AlgorithmESP512 and AlgorithmEd25519EdDSA are added
• EdDSA Signer and Verifier are changed to have alg field, and it is returned in Algorithm()
• deriveAlgorithm is changed to deriveAlgorithms, now it returns the slice of possible Algorithms (at least one Algorithm is included for better error handling)
• tests are extended to cover {ES256, ESP256} and {EdDSA, Ed25519EdDSA}