Added lighting engine module

- New lighting engine module which contains new data types Light and
Material. These data types and functions facilitates making a basic 3D
iluminated program with a light and a model.

- Added lighting engine module example (currently included in raylib.h;
it might be compiled by separate and include lighting.h in game source C
file).

- Corrected some opengl defines control structures and added some TODO
to fix raylib-opengl 1.1 source build (note: now source can be compiled
without errors, but rlglReadPixels() won't work properly).

Note: most of functions of phong version 330 shader are not in v100
shaders, so I couldn't write a version 100 phong shader. These functions
are included from version 150.

examples/resources/shaders/phong.fs

@@ -0,0 +1,76 @@
+#version 330
+
+// Vertex shader input data
+in vec2 fragTexCoord;
+in vec3 fragNormal;
+
+// Diffuse data
+uniform sampler2D texture0;
+uniform vec4 tintColor;
+
+// Light attributes
+uniform vec3 light_ambientColor = vec3(0.6, 0.3, 0);
+uniform vec3 light_diffuseColor = vec3(1, 0.5, 0);
+uniform vec3 light_specularColor = vec3(0, 1, 0);
+uniform float light_intensity = 1;
+uniform float light_specIntensity = 1;
+
+// Material attributes
+uniform vec3 mat_ambientColor = vec3(1, 1, 1);
+uniform vec3 mat_specularColor = vec3(1, 1, 1);
+uniform float mat_glossiness = 50;
+
+// World attributes
+uniform vec3 lightPos;
+uniform vec3 cameraPos;
+
+// Fragment shader output data
+out vec4 fragColor;
+
+vec3 AmbientLighting()
+{
+   return mat_ambientColor * light_ambientColor;
+}
+
+vec3 DiffuseLighting(in vec3 N, in vec3 L)
+{
+   // Lambertian reflection calculation
+   float diffuse = clamp(dot(N, L), 0, 1);
+   
+   return tintColor.xyz * light_diffuseColor * light_intensity * diffuse;
+}
+
+vec3 SpecularLighting(in vec3 N, in vec3 L, in vec3 V)
+{
+   float specular = 0;
+
+   // Calculate specular reflection only if the surface is oriented to the light source
+   if(dot(N, L) > 0)
+   {
+      // Calculate half vector
+      vec3 H = normalize(L + V);
+      
+      // Calculate specular intensity
+      specular = pow(dot(N, H), 3 + mat_glossiness);
+   }
+   
+   return mat_specularColor * light_specularColor * light_specIntensity * specular;
+}
+
+void main()
+{
+    // Normalize input vectors
+    vec3 L = normalize(lightPos);
+    vec3 V = normalize(cameraPos);
+    vec3 N = normalize(fragNormal);
+    
+    vec3 ambient = AmbientLighting();
+    vec3 diffuse = DiffuseLighting(N, L);
+    vec3 specular = SpecularLighting(N, L, V);
+    
+    // Get base color from texture
+    vec4 textureColor = texture(texture0, fragTexCoord);
+    vec3 finalColor = textureColor.rgb;
+    
+    fragColor = vec4(finalColor * (ambient + diffuse + specular), textureColor.a);
+}

examples/resources/shaders/phong.vs

@@ -0,0 +1,28 @@
+#version 330
+
+// Vertex input data
+in vec3 vertexPosition;
+in vec2 vertexTexCoord;
+in vec3 vertexNormal;
+
+// Projection and model data
+uniform mat4 projectionMatrix;
+uniform mat4 modelviewMatrix;
+uniform mat4 modelMatrix;
+
+// Attributes to fragment shader
+out vec2 fragTexCoord;
+out vec3 fragNormal;
+
+void main()
+{
+    // Send texture coord to fragment shader
+    fragTexCoord = vertexTexCoord;
+    
+    // Calculate view vector normal from model
+    mat3 normalMatrix = transpose(inverse(mat3(modelMatrix)));
+    fragNormal = normalize(normalMatrix * vertexNormal);
+    
+    // Calculate final vertex position
+    gl_Position = projectionMatrix * modelviewMatrix * vec4(vertexPosition, 1.0);
+}