Send checkpoints when stepping or pausing in trace mode

[MaartenS11]

This works better for debuggers such as MIO which expect information about the current program counter/program state while stepping.

Also now resets the instruction counter upon using reset in the debugger so this no loner happens:

CHECKPOINT {"instructions_executed": 17, "fidx_called": 1, "args": [21], "returns": [-2], "snapshot": {"pc":241}}
EMU: chip_digital_write(10,0) 
EMU: 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
EMU: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
EMU: chip_digital_write(11,1) 
EMU: 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
EMU: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
Interrupt: 13
Reset WARDuino.
04
Interrupt: 4
CHECKPOINT {"instructions_executed": 13, "snapshot": {"pc":213}}
STEP!

Here we reset and then execute one instruction but say we executed 13. This should now be resolved.