Ensure a binary is generated during testing

This doesn't really do anything, but it makes test failures because of
Chisel compile failures (which don't actually return an error
message!).
Reset registers in the Flo backend

This has two advantages: it correctly handles the new vcd2step (which
outputs a few reset cycles) and it matches with the Chisel output.
Now both the Chisel and Flo backends reset all registers to 0.
Port to the latest libflo

This is actually a pretty small change, there's just a new Flo opcode
(DIV) that I'm currently not handling at all.