Add standard lighting (2/3)

- 3 light types added (point, directional, spot).
- DrawLights() function added using line shapes.
- Standard lighting example added.
- Removed useless struct variables from material and light.
- Fixed light attributes dynamic locations errors.
- Standard vertex and fragment shaders temporally added until rewrite it
as char pointers in rlgl.
TODO:
- Add normal and specular maps calculations in standard shader.
- Add control structs to handle which attributes needs to be calculated
(textures, specular...).
- Adapt standard shader to version 110.
- Rewrite standard shader as char pointers in rlgl.

examples/resources/shaders/standard.vs

@@ -0,0 +1,23 @@
+#version 330 
+
+in vec3 vertexPosition;
+in vec3 vertexNormal;
+in vec2 vertexTexCoord;
+in vec4 vertexColor;
+
+out vec3 fragPosition;
+out vec2 fragTexCoord;
+out vec4 fragColor;
+out vec3 fragNormal;
+
+uniform mat4 mvpMatrix;
+
+void main()
+{
+    fragPosition = vertexPosition;
+    fragTexCoord = vertexTexCoord;
+    fragColor = vertexColor;
+    fragNormal = vertexNormal;
+
+    gl_Position = mvpMatrix*vec4(vertexPosition, 1.0);
+}