Vendorizing pyyaml because pyyaml.org is down so often.
Removing PyYAML as a non-vendorized dependency.
Moving to vendorized yaml.
Merge branch 'master' into circular

* master:
  Moving to vendorized yaml.
  Removing PyYAML as a non-vendorized dependency.
  Vendorizing pyyaml because pyyaml.org is down so often.