Add byte array to Values message

Nobody has claimed this yet.

We currently do not have a way to properly encode byte arrays as the value of an attribute. Ideally, this would not be an allowed type but I can see in some rare cases where this might be useful. I would like to propose adding `bytes` as the 8th value message and specifically state that it may be ignored in the decoder.

I know that from an data format standpoint that protobuffers do not have any difference between bytes and strings, however, I have come to realize that in some situations such as the python protobuf libraries it attempts to enforce a text encoding type on the values as they are set via the protobuf library. Additionally, it would be ideal for a client to know if there is a non standard string format that it could be ignored for situations where a bytes field is being used.

Thoughts?

/cc @ericfischer @joto

Review the Values message definition and the decoder behavior described in the issue, then read the existing comment discussion before deciding whether a bytes value belongs in the specification. Done means reaching and documenting a decision on the eighth value type and how decoders should handle it.

Written by the indexing model from the issue text.