Lazy API loading

I added lazy api loading using the [`lazy-api`](https://github.com/IonicaBizau/node-lazy-api) module.

> ## Philosophy
> Having a big service API wrapper written in NodeJS, most of people create
> a `for` loop and load all API files before doing anything. The files are
> loaded in RAM. So, It's not so RAM friendly to load them this way.

> With the `lazy-api` module this issue is fixed. Lazy API loads the file
> when the API method is called. If an application only uses one file,
> only that file will be loaded in RAM. The other will not be loaded.

> <sup>[Source](https://github.com/IonicaBizau/node-lazy-api#philosophy)</sup>

I ran `npm test` and tests are passing.