Need canonical language documentation

We have some good tutorials, diagrams, etc, but we could really use a canonical grammar document that defines exactly what the PHDL syntax and semantics are. This is important because it:

1. Helps experienced users and developers by serving as a definite reference guide.
2. Explicitly defines how the language should work vs. how it actually works, so can drive and bound tests, refactoring, rearchitecting, etc.
3. Decouples PHDL as a language from PHDL as an implementation, which is important in promoting long-term adoption.
4. This has been demonstrated to be a critical feature of modern open source languages and is expected in any new language.