Fixed get_evolution when **kwargs are passed to firesong_simulation .
PL_Luminosity can now work for 2 sets of kwargs, (pl_lmin, pl_lmax, pl_alpha) or (pl_width, pl_alpha).
Removed zmax from StandardCandleSource and StandardCandleLuminosity. zmax is the simulation cutoff, should not be passed to the calculation of the standard candle. i.e., there are sources farther away then zmax which contribute to the diffuse flux, but we are not simulating them.
get_evolutionwhen**kwargsare passed tofiresong_simulation.PL_Luminositycan now work for 2 sets of kwargs, (pl_lmin,pl_lmax,pl_alpha) or (pl_width,pl_alpha).zmaxfromStandardCandleSourceandStandardCandleLuminosity.zmaxis the simulation cutoff, should not be passed to the calculation of the standard candle. i.e., there are sources farther away thenzmaxwhich contribute to the diffuse flux, but we are not simulating them.