Allow time-stamp patterns in fancy-log configuration instead of default HH:mm:ss

[watery]

Time-stamp accepts several patterns for the timestamp prefix, can fancy-log be made to receive them i.e. at module initialization?
It would be useful for multiday running applications.

[phated]

This is not a concern of fancy-log. gulp-cli is going to get theming support but it's complicated and not done yet.

Ref gulpjs/gulp-cli#63 and gulpjs/gulp-cli#137