[Feature Request] Allow for relative heights with -height

[driesceuppens]

What alias/snippet is this for?
For !map, !move and !go

Is your feature request related to a problem? Please describe.
When flying it can be a pain to track your height, mainly because needing to check what height you are at and then adding/subtracting the right amount can become a pain. This would solve that

Describe the solution you'd like
If your current height is 40 feet then !map -t <target> -height +30 would move you up 30 feet to a total of 70. It would be useful to be able to force either relative or absolute changes with some prefix like -height ~-30 always moves you to -30 feet.

Describe alternatives you've considered
There are no current alternatives.

Additional context
I made some code to change it and it currently looks like this

if height[0].isdigit():
  out[targ.name].update({'height':height})
else:
  newHeight = str(int(out[targ.name].get("height", "0")) + int(height))
  out[targ.name].update({"height": str(newHeight)})