v0.9

This will be a disruptive one, as we will need to change some API.
As LevelUp is going to remove WriteStream support from it, I _think_ we should do it too.

The current WriteStream implementation only use is by [LevelGraph-N3](http://github.com/mcollina/levelgraph-n3) to import huge loads of triples. In order to do so, LevelGraph uses level-writestream, a WriteStream alternative that can handle multiple concurrent batches: https://npmjs.org/package/level-writestream. That breaks the atomicity of putting all indexes in a single batch, but it's extremely efficient for write loads.

In the browser, having any WriteStream in will just increase the package size.

* [x] Upgrade Level-js and remove the patching
* [ ] Upgrade LevelUp to 0.19 and dump putStream and delStream
* [ ] Deprecate getStream in favor of readStream.
* [ ] Write a gaws (levelGrAph-WriteStream) module to add that functionality again, if someone needs it.
* [ ] Update LevelGraph-N3 and LevelGraph-JSONLD to not use `putStream` but leverage the new module, and/or a different solution.
* [ ] Multilevel support #60.
* [ ] remove `join()` and `joinSearch()`, which were deprecated in favor of `search()` and searchStream()`)

Any opinions? Consider this as a _proposal_, any volunteers for any of this?