As discussed in #2, ring is not mature enough to replace OpenSSL. Hence,
the standalone mode which has been made to implement such a replacement
has to be removed until ring becomes usable.
Until now, the crypto key abstraction used two different type: PublicKey
and PrivateKey. Unfortunately, it does not work with ring and should
therefore be rewrote with a single type: KeyPair.
Because ring does not currently support RSA keys generation, the default
algo must be adapted depending on whether or not the standalone feature
is activated.
Since it is planned to add a "standalone" feature that will replace
OpenSSL by crates not linking to any external library, it is required to
abstract all the OpenSSL specific types. This is a huge work and
therefore is divided in several steps. This first one is dedicated to
public and private keys.
rel #2