Support emitting B83/B84 bundles

TI-Connect CE supports bundles which are basically just zip archives, but it sends all of the contained variables in one shot. That would be convenient for users of this as well, since emitting zips from the webapp requires then extracting the zip and sending files individually.

Existing implementations:

• CEMU: read-only: https://github.com/CE-Programming/CEmu/commit/9094f817af2953ea20cf36cfe5b8973a05c94bb4#diff-60a4467bfd670926076b5a40271613d2bd2fca8064e7143214ffc2f8727071a3
• TI-boy CE: write-only: https://github.com/calc84maniac/tiboyce/blob/master/tiboyce-romgen/romgen.c

I've already implemented write-only support in tifiles 0.2.0.