add fitter tests, especially testing that bad params are rejected
add fitter tests, especially testing that bad params are rejected

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