Review RenderTexture drawing usage

Now `BeginTextureMode()` does not clean buffers automatically, that behaviour has been changed because there could be some case (i.e. painting software) where texture buffer does not ned to be cleared; user is responsible of clearing buffers using `ClearBackground()`

examples/shaders/shaders_custom_uniform.c

@@ -83,19 +83,21 @@ int main()
 
             ClearBackground(RAYWHITE);
             
-            BeginTextureMode(target);   // Enable drawing to texture
+            BeginTextureMode(target);       // Enable drawing to texture
+            
+                ClearBackground(RAYWHITE);  // Clear texture background
 
-                BeginMode3D(camera);
+                BeginMode3D(camera);        // Begin 3d mode drawing
 
                     DrawModel(model, position, 0.5f, WHITE);   // Draw 3d model with texture
 
                     DrawGrid(10, 1.0f);     // Draw a grid
 
-                EndMode3D();
+                EndMode3D();                // End 3d mode drawing, returns to orthographic 2d mode
                 
                 DrawText("TEXT DRAWN IN RENDER TEXTURE", 200, 10, 30, RED);
             
-            EndTextureMode();           // End drawing to texture (now we have a texture available for next passes)
+            EndTextureMode();               // End drawing to texture (now we have a texture available for next passes)
             
             BeginShaderMode(shader);
             
@@ -104,6 +106,7 @@ int main()
             
             EndShaderMode();
             
+            // Draw some 2d text over drawn texture
             DrawText("(c) Barracks 3D model by Alberto Cano", screenWidth - 220, screenHeight - 20, 10, GRAY);
             
             DrawFPS(10, 10);