Improved examples.

- Examples match those of https://github.com/jaydenseric/apollo-upload-examples.
- Added example cURL requests, fixing jaydenseric#6.
- Added example request payloads.

Fixed wrong field ordering in an example.

Added Prettier config.

Removed mention of the `files` multipart field.

Now the master branch accurately describes the current generation of implementations. An experimental new spec that uses a `files` field among other updates will be drafted soon as a PR.