refactor: better NO_COLOR support

[figsoda]

Fixes #62
Fixes #66

colors::* are now lazy statics that respect NO_COLOR instead of pure functions

• colors::yellow() -> *colors::YELLOW
• if *NO_COLOR_IS_SET is no longer needed outside of colors module

switched from lazy_static to once_cell since it doesn't use macros and the code can look a little cleaner

[marcospb19]

That's pretty good, loved the code.

You're solving not only #62, but also #66.

Thanks!

[figsoda]

Thanks for the review!
I edited to close that issue too