These two enums must have identical variants. One is generated from the
instruction formats in meta/cretonne/formats.py, the other defines the contents
of an instruction.
Emit a conversion from InstructionData to InstructionFormat which also serves
to verify the correspondence. Rustc will error is the match is not complete.
This is a no-payload enum which will have the same variants as InstructionData.
This makes it possible to talk about the format of an instruction without
actually creating an InstructionData instance.
Use a simple quadratically probed, open addressed hash table. We could use a
parfect hash function, but it would take longer to compute in Python, and this
is not in the critical path performancewise.
Generate nice doc comments for the Opcode enum variants that 'cargo doc'
will pick up.
Include a `Display` trait implementation that prints the lower
snake-case version of the opcode name.
