Function `colors_enabled`

pub fn colors_enabled() -> bool

Returns true if colors should be enabled for stdout.

This honors the clicolors spec.

CLICOLOR != 0: ANSI colors are supported and should be used when the program isn't piped.
CLICOLOR == 0: Don't output ANSI color escape codes.
CLICOLOR_FORCE != 0: ANSI colors should be enabled no matter what.