Pyyaml: Migrate canonical repo from BitBucket to GitHub

[ingydotnet]

@sigmavirus24 and @ingydotnet are taking over maintenance of pyyaml from @xitology.

The first step is to migrate the Mercurial repo on BitBucket to a Git repo on GitHub. We hope this will make for a truly collaborative community maintenance environment.

Here are the steps being taken:

1. Use GitHub import feature to migrate the repo into a temporary repo.
2. Delete the old tags from https://github.com/yaml/pyyaml
3. Rename old branches in https://github.com/yaml/pyyaml to old/$name
4. Fetch all branches and tags from newly imported repo into https://github.com/yaml/pyyaml
5. Push all new branches and tags to https://github.com/yaml/pyyaml

After this we will:

• Review the existing issues and pull requests
• Make new issues for all planned work
• Announce the changes to [email protected]
• Announce changes in blog post on http://yaml.io
• Reach out to packagers: Debian et al

See also yaml/libyaml#11

[ingydotnet]

Migration part is complete. @sigmavirus24 please review.