Can't access `mcmcP` output because `MHResult` is in a hidden module

[rihardsk]

Not exactly a bug, but probably an oversight?

Sampling with mcmcP produces samples wrapped in MHResult, but I can't access anything because MHResult (and Trace that's contained within) is defined in Control.Monad.Bayes.Traced.Common and monad-bayes doesn't export that module (there are no re-exports in other modules either).

[turion]

True. This should be taken into account when fixing #260.