Ol3-Cesium 1.6 release

Hello,

Just in time for June, I am pleased to announce version 1.6
of Ol3-Cesium, based on Ol 3.5.0 and Cesium 1.10.

This version brings many improvements, notably:
- clamping of points and texts to the terrain;
- feature to Cesium converter as a class;
- more powerful picking, for all geometries.

Please check the CHANGES.md for details.

Note that the OL3 version stayed unchanged in this version.

Thank you to all contributors of Ol3, Ol3-Cesium, and in particular to
the Cesium team for this great clamping to terrain feature.

In the next few months I will give two talks about Ol3-Cesium.
First at FOSS4G-Europe at Como in Italy on July 16th.
Then, together with Andreas Hocevar, at FOSS4G Seoul in Korea in September.

Looking forward to meeting you there.

Congrats on the release, Guillaume. Please send us links to the slides/videos of your talks, and we’ll help spread the word.

Patrick