Read output from the script as it comes and update the candidate
list progressively.
Disable updating of the list when a completion has been explicitely
selected.
This commit also introduces a regression in that I decided that the best way to
avoid overly long and confusing names was to rename the current shell-*
switches to script-*, and have the shell command completion be
shell-completion.
renamed script-{completion,candidates} to shell-script-*
Updated docs with new switch names
Added -shell-completion switch to x11-repl and kitty-repl
