splited tick to two functions

Hi visionmedia,

I know I can set the steam to store the output. But sometimes people wants to get the progress bar as a string. So they can handle it by themselves. For example: I want to draw a multi progress bar. I will maintain a progress bar array. print all the progress bars in the same time.

So I splited the function: tick into two functions "increase" and "toString"

You can take a look my code. It's not too much changes. And it can keep the old tick work correctly. But this change can give this lib new ability to give user current status manually.

If you think the function name is not good you can change it whatever you want.