replace very expensive get_udv_by_name lookup of dummy variables
optimize out another dummy variable lookup by name
boldface and italic markup for enhanced text
Include share and demo/games in GNUPLOT_LIB
error_ex() releases allocated memory
Fit converged if chisq == 0. An invalid covariance matrix is no longer fatal but indicates failure to converge.
Give advice on better initial parameter values than zero
default to "set fit errorvar"