Implemented caching for 'nodejs_latest_version' and 'nodejs_stable_version' facts. This should speed up the Puppet/Facter run (depends on location, but 'time facter -p' is roughly 5-6 sec faster). By default fresh versions are fetched once a day from nodejs.org. Though not a complete solution to #63, if a cached and recent versions exist in /tmp/puppetfacts/nodejs, this should also avoid problems when nodejs.org is down