Add contribution guidance

Add CONTRIBUTING.md that points to the same document in chef-cookbooks
Add mention of the contribution document in the top of the README.md
Merge pull request #136 from claco/contributing

Merged automatically by jenkins after successful build test
Make token expiration overridable

Required by rcbops-cookbooks/swift-private-cloud#27
Add cron job for token cleanup

closes rcbops-cookbooks/swift-private-cloud#27
Forgot a comma.  Duh.
Merge pull request #137 from rpedde-rcbops/token-cleanup

Merged automatically by jenkins after successful build test
Updating version # to 4.1.2