Fixes for dependencies

 * add dep for 'parent' https://rt.cpan.org/Ticket/Display.html?id=95430
 * make PPI optional https://rt.cpan.org/Ticket/Display.html?id=95316
 * add recommends for App::FatPacker (for author/maint)
 * whitespace tidying
Remove PPI as dependency

As per https://rt.cpan.org/Ticket/Display.html?id=95316

Have removed from `bin/require-perl-tags` too, which ends up with a
fatpacked file-size of 80K vers 800K, at the cost of PPI functionality.
Merge branch 'fix-dependencies'