underlying crypto implementation.
Modified proto.hpp to use the new CryptoAlgs types for
cipher/digest selection.
Added initial PolarSSL implementation for cipher/digest
selection using CryptoAlgs types.
Note: this implementation is incomplete, see fixmes.
three-level factory model:
CryptoDCFactory -- builds CryptoDCContext objects for a given
cipher/digest
CryptoDCContext -- builds CryptoDCBase objects for a given key ID
CryptoDCBase -- encrypt/decrypt data channel