a leveldb backend

I've written a tiny little backend using [leveldb](https://github.com/rvagg/node-levelup). Now when somebody posts a new message, their message is saved and written to leveldb. You can get at the data like this:

``` bash
$ curl http://localhost:8000/YOU/timeline.json
{"user":"YOU","time":1386470529,"timetext":"NOW","text":"it's like twitter but for all of history"}
{"user":"YOU","time":1386470533,"timetext":"NOW","text":"wooooo"}
{"user":"YOU","time":1386470649,"timetext":"NOW","text":"it's like twitter but for all of history"}
```