adding PKE interface

The patch adds PKE interface functions, namely:
    EVP_PKEY_encrypt_init
    EVP_PKEY_encrypt
    EVP_PKEY_decrypt_init
    EVP_PKEY_decrypt

Additionally it adds functions for getting and
setting public and private key to/from byte array.

	EVP_PKEY_get_raw_public_key
	EVP_PKEY_new_raw_public_key
	EVP_PKEY_get_raw_private_key
	EVP_PKEY_new_raw_private_key

Finally it also adds a function for getting NID
of a scheme by it's name (SN).