NO_COLOR support

[kucharskim]

I see many projects using this library, and I don't see simple way to disable colored output for those apps (without code modification). In production environments I like to grep easily logs and colors are making it super difficult.

More info about NO_COLOR environment variable at https://no-color.org/

[AndreasBackx]

If NO_COLOR support is added, might be additionally good to add support for CLICOLOR_FORCE which allows you to always enable it. See http://bixense.com/clicolors/.

[docwhat]

The good thing about standards is that there are so many to choose from.
  - Andrew Tanenbaum