Add support for "application/hal+json" Content-Type

[davidyscott]

Is your feature request related to a problem? Please describe.
Working with a HATEOAS service that uses HAL, I would like to be able to make requests with the "application/hal+json" media type.

Describe the solution you'd like
I would like an additional option from the content type dropdown.

Additional context
I believe I have made the necessary code changes, but as the CONTRIBUTING.md file for this repo has no information, I'm not sure how to submit the PR.

[liyasthomas]

If you believe you've made necessary changes to solve this issue, go on and make a PR. The contributing guidelines for this repo are still a WIP

[davidyscott]

@liyasthomas Done, #90, thanks!