Browserifiable.

Hopefully this PR creates a browser branch in the main repo(!)

I managed to squash my commits but I haven't worked out how to clear out the old (and crappy) messages, sorry.

In other news:
+ I fixed all those timeout tests just by changing approximateSize again https://github.com/maxogden/level.js/issues/11 although it's probably not as good/optimal as what you were thinking
+ Those two .del tests fail still but by adding `'sync':true` into the test they cause `Error: timeout of 2000ms exceeded` too
```
it("should remove one and still return the other", function(done) {
      db.del(triple2,{'sync': true}, function() {
```