peru.yaml for deps and raw modules in third-party/

Place raw modules into third-party/ and use peru to update checked in deps. The yaml module from pyyaml is checked in directly beneath third-party/. Updating deps would look something like:
1.) update peru.yaml
2.) peru sync --force
3.) run tests
4.) commit

A test could be added to compare checked in dep trees against trees fetched by peru. This change continues to use pyyaml 3.10.