Interpret weighted prompts

[0x2b3bfa0]

This pull request ports the weighted subprompts syntax mentioned at #35 (comment) from sd-webui/stable-diffusion-webui.

grabs all text up to the first occurrence of : uses the grabbed text as a sub-prompt, and takes the value following : as weight if : has no value defined, defaults to 1.0 repeats until no text remaining

Source

• https://github.com/yue-here/sd-walker/blob/053437abff5fba92ce8c6f0383268d553448ad7e/txt2img_generator.py#L155-L166
• https://github.com/sd-webui/stable-diffusion-webui/blob/010b27ce9af3ee22758a0cf2650383525cb44a7b/optimizedSD/optimUtils.py#L5-L48

Warning
Admittedly, ldm.util is not the best place to paste that function; feel free to suggest a better place.