Compute the u16 representation of encoding lists and emit a big table
concatenating all of them. Use the UniqueSeqTable to share some table space
between CPU modes.
Amend build script to generate an encodings-<isa>.rs file for each target ISA.
Emit a function that can evaluate instruction predicates.
Describe the 3-level tables used for representing insrruction encoding tables.
Add Python classes representing the tables.
The generated code is incomplete and not used anywhere yet.
