Accessor function for public key structure in mbedtls_ecp_keypair

[stevew817]

Suggested enhancement

Either a direct accessor function to retrieve the public component of an mbedtls_ecp_keypair, or a function to write out the public key to a binary buffer. Similarly, a way to create an mbedtls_ecp_keypair structure containing only the public part of the key.

Justification

Mbed TLS needs this because the public key component was made private.

[mike-rus]

@stevew817, Just to clarify the issue, the public part of the key consists of two ECP point coordinates, do you suggest returning them separately or concatenate them to one common binary buffer?