Export WriteStream and switch constructor args

Now just exports `WriteStream` to encourage users not to monkey patch (I think we need to get away from this practice), but I've replaced it with a `patch()` export that'll put `createWriteStream()` back on if you want it.

Also switched the arguments to put the optional `options` object second:

```
var ws = new WriteStream(db, options)
```

Fixed up tests, did some minor formatting, cleaned up dependencies.

Ready for a 1.0.0 unless I get some disagreement.