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.
Clarify the textual encoding of floating point numbers.
Don't allow decimal floating point since conversion to/from binary can produce
rounding problems on some (buggy) systems.
