diskbb: accretion disk, multi-black body components

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The spectrum from an accretion disk consisting of multiple blackbody components. For example, see Mitsuda et al. (1984) or Makishima et al. (1986).

par1	temperature at inner disk radius (keV)
norm	$(R_{in}/D_{10})^2 \cos\theta$ , where where $R_{in}$ is “an apparent” inner disk radius in km, $D_{10}$ the distance to the source in units of 10 kpc, and $\theta$ the angle of the disk ( $\theta = 0$ is face-on). On the correction factor between the apparent inner disk radius and the realistic radius, see e.g., Kubota et al. (1998).