Add functions to the library for performing the sampling #45
Description
We currently rely on a lot of custom code that only appears in sample_maps.py for doing the sampling. This is not good. So for instance, if a user wants to sample a map in a notebook, they have to redefine everything.
We should add a set of functions to the library, so that you can for instance easily get the likelihood, and then just provide the likelihood and prior to a function that obtains samples for you.