added ALFALFA source reader
added ALFALFA source reader

e-koch/pyspeckit,jpinedaf/pyspeckit,dinossimpson/pyspeckit,low-sky/pyspeckit,jpinedaf/pyspeckit,low-sky/pyspeckit,keflavich/pyspeckit,dinossimpson/pyspeckit,mikelum/pyspeckit,allisony/pyspeckit,mikelum/pyspeckit,bsipocz/pyspeckit,allisony/pyspeckit,pyspeckit/pyspeckit,e-koch/pyspeckit,bsipocz/pyspeckit,pyspeckit/pyspeckit,keflavich/pyspeckit,vlas-sokolov/pyspeckit,keflavich/pyspeckit-obsolete,vlas-sokolov/pyspeckit