Add a renderToStream method

[karaggeorge]

I'm working on a package and I need to render a component temporarily (like renderToString does) but I need the lifecycle events to occur and emit the updates to a stream. However, I don't need the stdin hooks for escape, Ctrl+c etc. Plus, when I call unmount, I don't want the program to exit.

Right now, as a workaround, I call render(<Component />, {stdout, stdin}) with my stdout being the stream I implement, and stdin being a Noop version of a Readable stream made to look like stdin. To unmount, I have to import call-tree directly and manually unmount, since calling the returned method of render ends my process.

I think implementing a method renderToStream that does the basic functionality without being bound to stdin/stdout is fairly easy, and then render could use that, and add the stdin interactions.

If that sounds like a good idea, I can write a PR.
If there is an easier way to do this that I'm not seeing, let me know.

Also, I think it would make sense to be passing the updated component by itself (without the eraseLine characters that the log-update uses to clear the terminal)

[karaggeorge]

The purpose of this is a package that allows components to be rendered side-to-side (horizontally aligned):