Making of LLemMings

Bugfix: restore background proper when blowing them up

ChatGPT: prompt below

Human: Also added some floating combat messages

>>> Prompt:
Using javascript, I need a function that:
- creates a temporary 2d HTML canvas using same size as global variable 'canvas'
- calls this function on it: setGradients(context, gradients),
- takes a byte-array backup of it to return
- destroy the temporary canvas
- name the function backupGradients(gradients)