* generate key pair
* crypto: sign/verify functions
* remove extension
* parse/serialize keys
* use RSA recipient/sender keys (TODO sign/verify)
* make PublicKey newtype, assign 0s to private_p & private_q
* replace SMP command parsing with Attoparsec
* rename types: Signed->Transmission, Transmission->SignedTransmission
* sign and verify commands (server tests skipped, agent tests pass)
* SMP client: avoid seralizing transmission twice when sending commands
* update SMP server tests to use command signatures
* remove support for "SEND :msg" syntax from SMP server protocol
* rename RSA module name to R to avoid confusion with C used for S.M.Crypto
* update key sizes to use bits `div` 8
* tidy up