add a warning to inform users if they're trying to use something undefined
add a warning to inform users if they're trying to use something
undefined

jpinedaf/pyspeckit,low-sky/pyspeckit,keflavich/pyspeckit,low-sky/pyspeckit,pyspeckit/pyspeckit,pyspeckit/pyspeckit,jpinedaf/pyspeckit,e-koch/pyspeckit,e-koch/pyspeckit,keflavich/pyspeckit