[build][b2] Add colors support to echo rule and actions

From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2020-04-21 17:23:33

Hi,

I did an experimental UI/UX wank for B2:
https://github.com/boostorg/build/pull/573

If anyone is interested in this kind of thing,
then let's make B2 great again! ;)

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net