Log only the "Finished" messages and not the "Starting" ones

[marcofugaro]

Hey, it would be really useful if I could tell Gulp to log only when a task is done, not when it starts. I don't actually care when the task starts during development. I only care about how much time it took and if it ran successfully.

I've tried the log-level option and it just turns the starting/finished logs on or off.

What do you think?

[sttk]

@marcofugaro Now we consider that gulp-cli enable to customize colors and messages of logs. If it is achieved, gulp-cli will be able to output an empty line too instead of starting log.

[phated]

@sttk I think we should avoid logging any line that is "falsey" so they can set the theming to false to disable.

[sttk]

@phated To do that, we should modify lib/shared/log/log-levels.js in PR #161 as follows:

• L33: log.on(level, console.error); → log.on(function(s) { if (s) console.error(s): });
• L35: log.on(level, console.log); → log.on(function(s) { if (s) console.log(s): });