support for NO_COLOR env var #105

No, we've been asked this a bunch of times. This would add nothing; FORCE_COLOR is already a bit of a convention in the *nix world. We don't need 10 competing standards.

This is a pity, since there is disagreement about the meaning of FORCE_COLOR=0. The site https://force-color.org/ specifies (emphasis added):

When this variable is present and not an empty string (regardless of its value), it should force the addition of ANSI color.

Other projects cite this page and refuse to implement FORCE_COLOR=0 to disable color. NO_COLOR would be unambiguous.

@Qix- isn't the object of this library to account for the emerging standards through it's stated mission of

Detect whether a terminal supports color

The existing implementation is effectively already an attempt to account for a number of community standards around color support declarations using environment variables, of which NO_COLOR is simply another one to add?

There's no "standard" for any of this, and I don't see anywhere where we mention we'll add support for any idea that comes along.

This would add nothing...

This would add something I believe, since: - https://no-color.org/; - Symfony and Laravel PHP frameworks use the env. variable for VarDumper; - Node supports it even too.