interface with mashr

[stephens999]

we should document how to use this with mashr, probably in the mashr vignette?
It may require writing a function or functions to produce mashr objects (priors?) in the udr package?

[pcarbo]

Yes, that's a good idea, but perhaps it makes sense to tackle Issue #21 first, and then illustrate the (more user-friendly) interface in the vignette.