Add support for `--no-color` and `$NO_COLOR`

[Arinerron]

options:

• write a wrapper for fprintf to strip ANSI maybe?
• provide an alternate non-color string in every logging function?
• make a COLOR() printf macro and split out every color into separate printfs?
• use %s and (OPT_NO_COLOR ? "" : COLOR_...)?

[Arinerron]

COLOR() printf might be best so we can collect nbytes_written += printf(...) in the future when we align stuff with nbytes

[Arinerron]

7f70389