New 'ids' command, and stdin reading

- New 'ids' command that returns a filtered set of task ID numbers, instead
  of the actual tasks.  For advanced pipeline use.
- Now supplements the command line with data read from standard input, which
  allows commands like:  echo 'add Pay the bills' | task

test/hook.format-prompt.t

@@ -56,7 +56,7 @@ if (open my $fh, '>', 'hook')
 my $output = qx{../src/task rc:hook.rc version};
 if ($output =~ /PUC-Rio/)
 {
-  my $output = qx{echo "\\nquit\\n" | ../src/task rc:hook.rc shell};
+  my $output = qx{echo "-- \\nquit\\n" | ../src/task rc:hook.rc shell};
   like ($output, qr/<foo>/, 'format-prompt hook prompt -> <prompt>');
 }
 else