voigt: Voigt line profile

A simple Voigt line profile. The Voigt profile is the convolution of a Gaussian and a Lorentzian.

The parameters are:

par1	$E_l$, line energy in keV
par2	$\sigma$, gaussian line width in keV
par3	$\gamma$, lorentzian FWHM line width in keV
Norm	$K$, total photons/cm$^{-2}$/s in the line

Both the gaussian and lorentzian lines are truncated at the point that the integrated flux under the line is within a critical value of the total flux. This critical value can be changed using xset LINECRITLEVEL. The default critical value is $1.0\times10^{-6}$.