kdblur: convolve with the laor model shape

A convolution model to smooth a spectrum by relativistic effects from an accretion disk around a rotating black hole. Uses Ari Laor's calculation including GR effects (Laor 1991). Modified from laor model by Andy Fabian and Roderick Johnstone.

par1	Index: power law dependence of emissivity (scales as $R^{-par1}$)
par2	inner radius (units of $GM/c^2$)
par3	outer radius (units of $GM/c^2$)
par4	inclination (degrees)