Imports of package session

PathSynopsis
go.mau.fi/libsignal/eccPackage ecc provides a way to generate, sign, and use Elliptic-Curve X25519 Cryptography keys.
go.mau.fi/libsignal/keys/chainPackage chain provides chain keys used in double ratchet sessions.
go.mau.fi/libsignal/keys/messagePackage message provides a structure for message keys, which are symmetric keys used for the encryption/decryption of Signal messages.