cemekl, cevmkl: plasma emission, multi-temperature using mekal

A multi-temperature plasma emission model. Emission measures follow a power-law in temperature ( $dEM = (T/T_{max})^{\alpha-1}dT/T_{max}$).The switch parameter determines whether spectrum is calculated by running the mekal code, by interpolating on a pre-calculated mekal table, or using the apec model. The final option is now preferred.

For the cemekl version, the abundance ratios are set by the abund command. The cevmkl variant allows the user to define the abundances. The reference for this model is Singh et al. (1996, ApJ, 456, 766).

For cemekl the parameters are:

par1	$\alpha$, index for power-law emissivity function
par2	$T_{max}$, maximum temperature
par3	$n_H$ (cm$^{-3}$
par4	Abundance relative to Solar
par5	z, redshift
par6	Switch (0 = calculate, 1 = interpolate, 2 = interpolate using APEC model).
norm	Normalization

For the cevmkl variant the parameters are:

par1	$\alpha$, index for power-law emissivity function
par2	$T_{max}$, maximum temperature
par3	$n_H$ (cm$^{-3}$
par4-17	Abundances of He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command)
par18	z, redshift
par19	Switch (0 = calculate, 1 = interpolate, 2 = interpolate using APEC model).
norm	Normalization