Adding independent values for R, G and B brightness.

When doing a project that uses 3V batteries I noticed that the blue gets very weak when voltage drops. Having independent values of brightness for R, G and B and making them different (in my case 20, 32 and 128) solved the problem.

This is backwards compatible as it still has the setBrightness method that takes one parameter. The only problem I solved in a non ideal way was the getBrightness method.