Add README, simplify some logic, make blank line separator easier to configure alongside objectMode

Here's a variety of cleanup, mostly focused on getting clean single-line chunks in objectMode. Found this package today since it had the name I was gonna use if I couldn't find a nice simple "split a stream into lines" implementation already. So I figured I'd just run with yours ;-) Also added a README for good measure.

If this looks good to you, perhaps you could bump the package version and republish? (It should be fully backwards compatible, but might be worth a 0.2.0 since it's more than/not a bugfix.)