Nice skyLoc priors

When doing followup of externally triggered events (cf. GRBs) their sky locations are often specified as a RA-dec point with an error radius. It'd be good to be able to specify this as a prior on the sky, either as a simple unimodal Gaussian where the error radius is interpreted as the Gaussian's standard deviation, or as a correlated Gaussian (but that's probably overkill for this simple model). Care would have to be taken about the general cyclic nature of the RA-dec parameters such that the RA = 0 = 2pi or dec = |pi/2| points doesn't mess things up.

It'd also be good, ie even better!, to be able to read in a FITS file directly as the sky prior.