Update swagger.yml

[marksou]

Added code samples to Keys and Batch Requests section descriptions. Few other text edits. Views fine on my local Hugo.

Before submitting a pull request, please make sure the following is done...

1. Fork the repo and create your branch from the latest master.
2. If you've added code that should be tested, add tests!
3. If you've changed APIs, describe what needs to be updated in the documentation.
4. Ensure the test suite passes (go test).
5. Make sure your code lints (go fmt && go vet).