Fluent-Style API for DisableColor/EnableColor

[sp3c73r2038]

This will enable usage like

var red = color.New(color.FgRed).Add(color.Bold).EnableColor().Sprint

fmt.Println(red("I'm red."))

[fatih]

Hi @aleiphoenix

You can already use this style with something like:

red := color.New(color.FgRed).Add(color.Bold).SprintFunc()
fmt.Println(red("I'm red."))

Do I miss something with your PR maybe? Also this is a breaking change. None of the functions signature should change.

Closing this for now, but feel free to re-open an issue if you want to discuss it further. Thank you for your contribution.