Add support for generating bindings for token contracts.

[overcat]

fix #7

if __name__ == '__main__':
    rpc_server_url = "https://soroban-testnet.stellar.org:443"
    network_passphrase = Network.TESTNET_NETWORK_PASSPHRASE
    alice_kp = Keypair.from_secret(
        "SAAPYAPTTRZMCUZFPG3G66V4ZMHTK4TWA6NS7U4F7Z3IMUD52EK4DDEV"
    )  # GDAT5HWTGIU4TSSZ4752OUC4SABDLTLZFRPZUJ3D6LKBNEPA7V2CIG54
    bob_kp = Keypair.from_secret(
        "SAEZSI6DY7AXJFIYA4PM6SIBNEYYXIEM2MSOTHFGKHDW32MBQ7KVO6EN"
    )  # GBMLPRFCZDZJPKUPHUSHCKA737GOZL7ERZLGGMJ6YGHBFJZ6ZKMKCZTM
    native_token_contract_id = "CDLZFC3SYJYDZT7K67VZ75HPJVIEUVNIXF47ZG2FB2RMQQVU2HHGCYSC"
    client = Client(native_token_contract_id, rpc_server_url, network_passphrase)
    te = client.transfer(alice_kp.public_key, bob_kp.public_key, 1000, alice_kp.public_key, alice_kp)