Fix Writer failing with assertion error

```
AssertionError: can only buffer a finite number of bytes > 0, got "0"
writer.js:86:  this._bytes(0, this._writeHeader);
```

I'm guessing stream-parser has been updated since this code was written. The simplest way I could find to get the Writer working was bypassing stream-parser and implementing the through stream directly. 

Hopefully I haven't just missed something obvious here.