Add support for disabling colors

[ad-si]

LayoutOptions should have a layoutColor field that lets you output the document without any colors. Another option could be to automatically read the NO_COLOR env variable as described in https://no-color.org/

[lehmacdj]

Color isn't really a property of the layout since annotations are preserved unchanged in SimpleDocStream ann after layout but before rendering, e.g. when using layoutPretty.

You can easily ignore colors in a SimpleDocStream AnsiColor by using unAnnotateS :: SimpleDocStream a -> SimpleDocStream xxx which removes all annotations and would thus remove all colors. If you have a mix of annotations you want to preserve you can also use reAnnotateS to remove colors without too much difficulty.

[sjakobi]

We could consider checking for NO_COLOR or at least adding documentation about it in prettyprinter-ansi-terminal.

I'm more inclined towards documentation.