This new option forces pretty (non-raw/non-JSON) output. By default, when
not using a tty, swaymsg outputs using the "raw" format. This makes it
impossible to, for example, pipe the pretty output to a pager such as
`less` since piping does not use a tty.
The new -p/--pretty option gives the user explicit control over the output
format while retaining the default tty-dependent behavior.
Signed-off-by: Peter Grayson <pete@jpgrayson.net>