simplify reading of EC keys

[kleinmrk]

This MR slightly changes how EC keys are read.

Currently, both private and public keys are read (if provided), but the public key has no effect and the internally used openssl structure is overridden by the private part. Thus the public key has no effecton the final ecdsa object other than possibly throwing exceptions in the constructor.

This MR reads the keys the same way as they are read for RSA key, i.e., prefer private key if present, and completely ignore public part.

I also switched from PEM_read_bio_EC_PUBKEY to PEM_read_bio_PUBKEY, and from PEM_read_bio_ECPrivateKey to PEM_read_bio_PrivateKey. This change made it obvious that one could use the same code for reading RSA and EC keys. The functions only differ in type of errors they report, e.g., error::ecdsa_error::create_mem_bio_failed vs. error::rsa_error::create_mem_bio_failed.

[prince-chrismc]

We should deprecate/remove the older helpers and rename them to have RSA in the name.

jwt-cpp/include/jwt-cpp/jwt.h

Line 581 in b8e55e2

inline std::shared_ptr<EVP_PKEY> load_public_key_from_string(const std::string& key,

jwt-cpp/include/jwt-cpp/jwt.h

Line 625 in b8e55e2

inline std::shared_ptr<EVP_PKEY> load_private_key_from_string(const std::string& key,