update readme to reflect some recent changes

prevent extra network tabs from putting images into wrong prompts
prevent settings leaking into prompt

remove random artist built-in extension (to re-added as a normal extension on demand)
remove artists.csv (but what does it mean????????????????????)
make interrogate buttons show Loading... when you click them

rework of hypernets: rather than via settings, hypernets are added directly to prompt as <hypernet:name:weight>

internal progress relative path

Fixes minor typos around run_modelmerger

Update shared.py