Previously fonttools was choosing between the optimal opcode
from PUSHB, NPUSHB, PUSHW, and NPUSHW. We now respect
whatever was requested and err if the format doesn't support
the data.
Morevoer, if the number of numbers to push is more than 255,
we add multiple push instructions to push all the numbers.
Finally, add a new pseudo-opcode "PUSH" that automatically
chooses the best format.
This, by itself, reduces roundtrip noise by not optimizing
the bytecode as it was before. In a followup commit I'll
change the bytecode disassembler to always produce PUSH
in the textual instructions instead of the four variants.
That way, we get both the optimization during assembling,
and reduced noise in XML.
Part of https://github.com/behdad/fonttools/issues/73
3714c78c92