V1: Give RGB LED a random color at start.
V2: RGB LED's color changes every 0.5 second.
V2.5: Extract `setLed(int ledPin, int color)` function.

Eliminates duplicated code inside function `setup` and function `loop`.
V3.1: Create two arrays to hold LEDs' current and target values.

Give random color values to LED when starting and store it in currentValues.
Generate another set of random colors to be targetValues.
V3.2: Add decomposed steps of transition in loop.