Add interrupt method

[RodEsp]

The interrupt method allows the user to maintain a the spinner on a single line while writing new messages to the output.

This addresses #49 to a degree. It only allows you to print lines above the spinner, not below. But at least your spinner isn't duplicated on different lines.

[kbrandwijk]

Any chance of getting this merged? Would really help my use case too...

[sindresorhus]

The code looks good, but I'm not sold on the method name. interrupt makes it sound like the spinner is actually interrupted, but it's the opposite. Can someone think of a better name?

[kbrandwijk]

It's similar to what other progress libraries use. I've used https://github.com/visionmedia/node-progress a lot in the past, it has exactly the same interrupt() method.

[RodEsp]

Doesn't really matter to me. interject() or interpose() could be good alternatives or even just insert().

[kbrandwijk]

or log(), or out() or ...

[novemberborn]

#69 makes it so .clear() can be called followed by .render(). This means you can clear the current spinner, write new lines, and then re-render the spinner. I think that solves the original use case.