Create test vectors for interroperability with drand/tlock and drand/tlock-js

tlock-rs should be interroperable with other implementations. It would be good to have shared test vectors, as mentioned in drand/tlock#77

This could include
* encoding on multiple networks, both on G1 and G2, with possible custom domains
* Encoding for round 1, and max round
* A set of malformed age stanza?