Add some change.

Hi, Lukasz.
I'm very interested in onigiri and add some change.

+ add test(use mocha and travis ci)
+ fixed global leak(global variable)
+ declare methods in prototype
+ add argument 'option' for find method. 

```js
// select first match element
var firstUser = db.find('users', {
    age: 25
}, "first");

// select first match element
var lastUser = db.find('users', {
    age: 25
}, "last");
```
I hope you can understand my english,
My english isn't good ....