Add scaling factor for timeline, custom render popup function, prop documentation

[brianweiner]

Cool library! We needed something that displayed in a gantt-like manner without any actual management behaviors.

I took a shot at documenting the props. I was going to add another column for defaults / examples, but thought maybe you'd have some comments first.

We needed custom messaging for the popup, I added a renderPopup prop for GanttRow so we could pass a curried function in that let us combine row-specific details into the rendered message. We thought maybe this would be useful for other users as well.

Also had some issues with the calculated # of ticks -- I ended up just using a simple scaling factor to increase the # that was calculated.

You won't offend me if you reject :)

[clayrisser]

Could you separate the documentation into a separate pull request?

[brianweiner]

Sure np #14

[clayrisser]

It might be a week before I finally get to review this

[clayrisser]

Thanks for the prop documentation