Language for specifying P4_16 architectures

[jafingerhut]

I talked about this topic at an earlier P4 LDWG meeting. Creating this issue to track any progress on the topic. Here is a link to my published work on this: https://github.com/jafingerhut/p4-guide/tree/master/specifying-p4-architectures

[smolkaj]

I'm very excited to see people pursue this direction!