This should offer a more reliable means of running `whitespace-cleanup`
on buffer save than whitespace-mode's whitespace-action setting. Also it
allows for easily toggling whitespace clean up off by disabling
whitespace-clean-mode.
Previously prettier would always format markdown files to 80 character
long lines. Now it reads the character width from the fill-column
variable in such a way that fill-column can be set with dir-local
variables.
This allows specific major-modes to disable hl-line-mode, which is
desired some terminal/shell modes like vterm where the hl-line flickers
constantly while typing.
