Fixes #1656

Only build the parser once (at import time) instead of for each step.

doctest is run by simply executing modules/prompt_parser.py

#1484 fix empty styles pattern

Add --use-cpu command line option

Merge branch 'cpu-cmdline-opt' of https://github.com/brkirch/stable-diffusion-webui into cpu-cmdline-opt

Remove MPS detection to use CPU for GFPGAN / CodeFormer and add a --use-cpu command line option.

Unexpected behavior when using eta = 0 in something like XY, but your default eta was set to something not 0.

#1484 fix empty styles pattern