Feature request: NO_COLOR standard implementation

[hellishvictor]

Hi, it would be great implement the NO_COLOR standard on miller since there's many CLI already with it and save the users from use "color=never", "--monochrome-color" or whatever.

Command-line software which adds ANSI color to its output by default should check
 for a NO_COLOR environment variable that, when present and not an empty string
 (regardless of its value), prevents the addition of ANSI color.

By adopting this standard, users that prefer to have plain, non-colored text output
 can export NO_COLOR=1 to their shell’s environment and automatically disable color
 by default in all supported software.

If your software outputs color by default, please consider not doing so. 

More info on: `https://no-color.org/`

Cheers

[johnkerl]

#1580 -- thanks @hellishvictor !