Made parpg-core the main repository to pull from and build. * Added parpg-assets as a subrepo under the data folder. * Moved the SConstruct script into parpg-core and modified it to build and install parpg-assets as well. * Made a few minor changes to the SConstruct file from the defunct parpg-main repository. * Modified unix parpg executable script template to be more forgiving of installing the parpg Python package outside of PYTHONPATH. * Updated the .hgignore file to include temporary SCons files.