Allow array of directories as input

All the directories to listen have to be passed as individual args.  

In case user wanted to read a list of directories from a config file and listen, he would typically load those directories as an array.  However, I can't pass the array of dirs.

Listen.to(["/dir/to/listen/to/one", "/dir/to/listen/to/two"])

To allow this, we just have to flatten the args.  This would keep the code backward compatibile and at the same time allow array to be supplied.