support filter by type & only show online services

Sorry, this feels like a lot... but here is the breakdown:

- support optional `type` that can be passed as first argument.
- add logic to change `type` **jpg** into **jpeg** for consistency with the `supports` array.
- add filter to only return services that are marked as online.
- tests! Using sinon to mock `request`.
- README.md updated with example and api for using `type`.
- `mochi` dep updated.
- `sinon` dep added.
- `npm test` hooked up to `node_modules` mocha :rainbow:.