Add support for RGB lights

[jtai]

Thank you for open sourcing this project and for the detailed protocol documentation. With them, I was able to sniff the commands sent to my Chihiros WRGB II and make the following changes to support RGB:

• Update create_manual_setting_command to take a color argument; it should be called once for each color channel
• Update the max_brightness argument in create_add_auto_setting_command to be a tuple of 3 ints, one for each color channel
• Update existing set-brightness and add-setting commands for the above changes
• Add new RGB versions of the above commands: set-rgb-brightness and add-rgb-setting
• Update README.md with RGB protocol notes and document the new commands

[TheMicDiet]

Hi @jtai, glad to see others using my project. Thank you for your contribution, RGB support is a nice feature :)