Merge branch 'dual-license-epl-2.0'

This merge commit changes the project's license from Apache License 2.0
to a dual-licensing model, allow the user to choose either
Apache License 2.0 OR Eclipse Public License 2.0.

This change is reflected in the license header of each source file as
well as in the NOTICE and README.md files.

The license change has been signed off by all former and present authors
of the project:
- Sebastian Heppner <sebastian.heppner@plt.rwth-aachen.de>
- Torben Miny (b. Deppe) <t.miny@plt.rwth-aachen.de>
- Leon Möller <leon.moeller@plt.rwth-aachen.de>
- Michael Thies <m.thies@plt.rwth-aachen.de>