Adds chaininstance, still not complete
Adds tests for chaining instance methods

(Almost) full example:

```js
Model.find(...).each().filter(function (inst1, inst2) {
  // ...
}).sort(function (inst1, inst2) {
  // ...
}).count(function (count) {
  // count instances
}).save(function (err) {
  // ...
}).get(function (instances) {
  // ...
});
```

These methods behave exactly as the native Array methods.
Merge pull request #40 from dresende/chaininstance

ChainInstance