Luigi

There were some conflicting libraries and unnecessary dependencies prohibiting SciLuigi from working with the latest Luigi 3.x branch.

This is now fixed, together with various cleanups and fixes in examples as well.

This release fixes various minor issues that were throwing errors with Python 3.7 and Luigi 2.8.

It now also suppresses a some specific warnings that are thrown because of the way SciLuigi uses Luigi's API, but which is tested to work as expected.

Fixes issue 41 - Thx to millawell and xaedes for the (simultaneous) PRs 40 and 42 .

Beta release. Many minor fixes, including a MANIFEST.in file, and updates in README.

Beta release. Updates in this release includes adjustments to be able to initiate workflow tasks from within workflow tasks.

See also [this release on PyPI](https://pypi.python.org/pypi/sciluigi/0.9.3b4).

Some notable changes in this release:
- Python 3 support
- Support for Amazon S3 data targets

Big thanks to jeffcjohnson for these contributions!