add custom event to let users programmatically update donut percentages

Signed-off-by: Marc MacLeod <marbemac@gmail.com>
Update README.md

Added live update info.
use colors array

Signed-off-by: Marc MacLeod <marbemac@gmail.com>
Merge branch 'master' of https://github.com/marbemac/donuts
Merge pull request #4 from marbemac/master

Ok, thanks!