Fix interface

before:
```javascript
var postcodeJp = require('postcode-jp');
var posts = postcodeJp({postcode: '003-1111'});
posts.addresses(function(callback){
  var address = callback[0];
});
```

after:
```javascript
var postcodeJp = require('postcode-jp');
postcodeJp.addresses({postcode: '003-1111'}, function(callback){
  var address = callback[0];
})
```