add flat text mode

[lgarrison]

We could add a mode to give a flat text (non-TUI) listing of the sizes and counts in the current directory.

[lgarrison]

Some ideas from @alexdotc:

cephdu should still retain the same defaults (TUI mode) with regular interactive usage, this would just be a flag.
Perhaps it should be the default if stdout is piped, redirected or otherwise not attached to a terminal device though. TUI output doesn’t make sense in that case
Unlike ls, output formatting is ideally consistent enough to be machine parsable by default