rdblur: convolve with the diskline model shape

A convolution model to smooth a spectrum by relativistic effects from an accretion disk around a non-rotating black hole. Modified from diskline model (Fabian et al. (1989)) by Andy Fabian and Roderick Johnstone.

Note that due to the energy binning the convolution process can produce spurious structures around sharp features in the spectrum being convolved. We strongly recommend testing for this by using the energies command to change the binning.

par1	Index: power law dependence of emissivity (scales as $R^{par1}$). If this parameter is 10 or greater then the accretion disk emissivity law $(1-\sqrt{6/R})/R^3$ is used.
par2	inner radius (units of $GM/c^2$)
par3	outer radius (units of $GM/c^2$)
par4	inclination (degrees)