ligo-skymap-contour - a new method to build a MOC credible region

I'd like to suggest a new method in ligo-skymap-contour in order to return a credible region in a Multi Order Coverage map (MOC). For doing this we need to import mocpy module. There is also a request to propose mocpy as an Astropy affiliated package. In more details, this new method can improve the interoperability from different software tools, in particular, from Aladin and ligo-skymap-contour - the user can create moc credible regions in ligo-skymap-contour and visualize them in Aladin. If you agree, I can open a merge request with a basic code for starting.