v0.9.0 with full PBR support and masked blending

This release adds an updated terrain material with full PBR support and experimental masked blending.
It also includes tools for editing, saving, building and importing TextureArrays, and new editor UI.
To keep the repo size down the example in the example folder doesn't include the texture assets.
You can download the assets here.
Extract the assets folder into the example folder so you end up with a path like example/assets.