pinspect: don't output newlines when no data is returned

Specifically when using `pinspect profiles` with the system, masks, or
unmasks options.
pinspect: add main command description
pinspect: add pkg_use, masked_use, and forced_use as profile subcmds

These output the related use flag settings from the cascaded profile
files as one would expect.
pinspect: use consistent subcommand descriptions