examples: add triangles scene

This scene showcases a transparent sphere.

examples/triangles.yaml

@@ -0,0 +1,91 @@
+# Optional field
+reflection_limit: 5
+
+camera:
+  origin: [0.0, 0.0, 0.0]
+  forward: [ 1.0, 0.0, 0.0]
+  up: [0.0, 1.0, 0.0]
+  fov: 90.0
+  distance_to_image: 1.0
+  x: 1080
+  y: 1080
+
+lights:
+  directionals:
+    - direction: [0.5, 0.5, 0.5]
+      color: {r: 0.0, g: 0.5, b: 0.0}
+    - direction: [0.5, 0.5, -0.5]
+      color: {r: 0.0, g: 0.0, b: 0.5}
+    - direction: [0.7, -0.5, 0.0]
+      color: {r: 0.5, g: 0.0, b: 0.0}
+
+objects:
+  - shape:
+      type: sphere
+      center: [5.0, -0.2, 0.2]
+      radius: 1.0
+    material:
+      type: uniform
+      diffuse:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+      specular:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+      transparency: 1.0
+      index: 1.9
+    texture:
+      type: uniform
+      color:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+
+
+  - shape:
+      type: triangle
+      corners:
+        - [10., -10., -10.]
+        - [10.,  10.,  10.]
+        - [10.,  10., -10.]
+    material:
+      type: uniform
+      diffuse:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+      specular:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+    texture:
+      type: uniform
+      color:
+        r: 1.0
+        g: 1.0
+        b: 0.0
+
+  - shape:
+      type: triangle
+      corners:
+        - [10., -10., -10.]
+        - [10., -10.,  10.]
+        - [10.,  10.,  10.]
+    material:
+      type: uniform
+      diffuse:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+      specular:
+        r: 1.0
+        g: 1.0
+        b: 1.0
+    texture:
+      type: uniform
+      color:
+        r: 0.5
+        g: 1.0
+        b: 0.5