rename to Test::Perl::Tags
extract guts of bin/perl-tags to App::Perl::Tags
bin/perl-tags work, inc --prune, --ppi flags

 * --prune flag, to avoid descending version-control directories
 * --ppi, with default to not use PPI (much faster)
 * change --depth default to 10, for speed
 * refactoring, documentation tweaks, and testing