add docs and docstrings for ammonia_hf model
add docs and docstrings for ammonia_hf model

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