zvfeabs: photoelectric absorption with free Fe edge energy

Redshifted photoelectric absorption with all abundances tied to Solar except for iron. The Fe K edge energy is a free parameter.

par1 equivalent hydrogen column (in units of $10^{22}$ atoms cm$^{-2}$)
par2 abundance relative to Solar
par3 iron abundance relative to Solar
par4 Fe K edge energy
par5 redshift z