Notable changes:
- Dropped Python 2.6 support. https://github.com/spotify/luigi/pull/934
- New experimental ["assistant"](https://github.com/spotify/luigi/blob/ac530c6cb3ac4df81ad236817373bdac19effa6d/luigi/interface.py#L104) feature.
- External tasks are now also registered. This might cause breakage in settings like described [here](https://github.com/spotify/luigi/pull/880#issuecomment-94008171)
- Many configuration settings have been hoisted to the new configuration system. Particularly for hdfs-related parameters. The `--help` command will show what new options are available.
- While `is_global` is not removed yet. It'll get removed anytime soon. Please use the new `positional=False` setting as a replacement in your parameters. In fact, we suggest to always use `positional=False`.
- The central scheduler now supports searching within groups. https://github.com/spotify/luigi/pull/903
- New dependency graph rendering using D3. https://github.com/spotify/luigi/pull/920
- The built in map reduce framework can now use `ujson` instead of doing `eval`. It's still not clear to us how much faster it is. https://github.com/spotify/luigi/pull/939
- Various bug fixes and other features.