NOTICE: osgEarth 3.0 released!

Friends, osgEarth 3.0 is tagged! The tag name is "3.0".

Thanks to everyone for their testing and support. As we've mentioned before, osgEarth has an overhauled API and earth file format, so be sure to consult the Upgrade Guide if you need help porting your application.

Release notes:

Version 3.0 (June 2020)
----------------------------
* Layer API overhaul - no more "Options/Config" structures; no more "drivers"
* Namespace overhaul - rolled Util/Features/Symbology/Annotation into the core
* ImGui integration - user intefaces - eventual replacement for "Controls"
* CompositeElevation/Image/LandCover Layers
* GrassLayer (splatting subsystem)
* Powerline Layer
* Wind Layer - add winds that will affect the GrassLayer
* Decal Layers - add geospatial decals to the terrain
* TiledFeatureModelLayer - fast feature rendering for pre-tiles data
* Arbitrary region invalidation and refresh for terrain engine
* Geocoder (OGR - optional build)
* LandCoverLayer - new fractal refinement
* 3D-Tiles Layer
* glTF support (partial, for 3D-Tiles)
* Cesium Ion Layer
* GDALDEM Layer - hillside shading, etc.
* NetworkMonitor tool
* WEBP loader - fast compressed imagery
* BASIS support - image compression
* DRACO support (GLTF) - geometry compression
* Support for >2GB ZIP files (new OSG ZIP plugin)
* Tracy integration - profiling
* Better error reporting infrastructure
* Performance improvements & bug fixes galore