Add previously deleted subroutine multi()

0.911 breaks existing code. The cause is the removal of the multi() subroutine.

What happens is that in 0.911, get("foo", "bar") returns empty Cisco::Reconfig objects for all "foo" that do not contain "bar", along with non-empty objects for those "foo" that do contain "bar". In 0.9, only non-empty objects were returned.