Add grey (and gray) as a defined colour for formatting about cli-ui

[lugray]

I'd be open to a PR adding grey as an alias for a bright black, but cli-ui is a terminal technology, not a web technology - the w3 color names don't apply. We use the ANSI color names: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors.

[colinbendell]

I'd like to suggest we add:

• black (90) //high contrast black (30)
• white (97) //high contrast white (37)

And then convenience aliases for:

• grey (90)
• gray (90)

Aside: might be worth having a 'default' as an alias for 'reset' (0) for the uninitiated in ANSI vernacular.

[lugray]

Closing as stale.