- Accept custom options.
- Break backwards compatibility on `PlatformAPI.connect` by removing
  the `username` parameter, since it never made any sense.
- Add notes about custom options to the README.
Merge pull request #8 from heroku/flexible-options-jkakar

- Accept custom options.

- Break backwards compatibility on `PlatformAPI.connect` by removing
  the `username` parameter, since it never made any sense.

- Add notes about custom options to the README.

- Update to the latest version of the schema, which includes
  `app.json` endpoints.

Fixes #3.
Fixes #4.
Fixes #5.