Added skybox example

Author: britzl

model/skybox/all.texture_profiles

@@ -0,0 +1,18 @@
+path_settings {
+  path: "**"
+  profile: "Default"
+}
+profiles {
+  name: "Default"
+  platforms {
+    os: OS_ID_GENERIC
+    formats {
+      format: TEXTURE_FORMAT_RGBA
+      compression_level: BEST
+      compression_type: COMPRESSION_TYPE_DEFAULT
+    }
+    mipmaps: false
+    max_texture_size: 0
+    premultiply_alpha: true
+  }
+}

model/skybox/example.md

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+---
+tags: model
+title: Skybox
+brief: This example shows how to create a skybox using a cubemap texture.
+author: Defold Foundation
+scripts: skybox.fp, skybox.vp
+---
+
+This example shows how to create a skybox. A skybox is a technique that makes the scene look bigger and more impressive by wrapping the viewer with a texture that goes around the camera 360 degrees.
+
+An in-depth explanation of skybox rendering can be found in [Tutorial 25 of OGL Dev](https://www.ogldev.org/www/tutorial25/tutorial25.html).
+
+
+Skybox texture from Babylon.js Playground (Apache 2 license)

model/skybox/example/assets/larger.png

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+right: "/example/assets/skybox_px.jpg"
+left: "/example/assets/skybox_nx.jpg"
+top: "/example/assets/skybox_py.jpg"
+bottom: "/example/assets/skybox_ny.jpg"
+front: "/example/assets/skybox_pz.jpg"
+back: "/example/assets/skybox_nz.jpg"