added hcn model (has been around for a week... why wasn't it in the repo?)
added hcn model (has been around for a week... why wasn't it in the repo?)

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