The Python Sky Model 3 software

Improvements to install documentation https://github.com/galsci/pysm/pull/93 Moved Github repository from healpy/pysm to galsci/pysm, under the Panexperiment Galactic Science group organization Changes in this release are related to the JOSS Review https://github.com/openjournals/joss-reviews/issues/3783 Turned UserWarning into logging, Pull Request 88 https://github.com/galsci/pysm/pull/8