Start adding tests

[gavanderhoorn]

As #76 highlighted, we need to start adding tests to important parts of the library to avoid regressions.

Initially I would suggest we focus on serialisation and deserialisation interfacing code, to document our expectations about the RWS msgs and make sure code layered on-top doesn't break when those messages change.

[jontje]

@gavanderhoorn, I edited your comment from "protobuf msgs" to "RWS msgs", since protobuf it not used in RWS communication 😉

[gavanderhoorn]

Thanks.

Too many things at the same time.