Use application/hal+json as default Content-Type and add to Accept header

[koenpunt]

Not every api accepts the application/json header.

[dblock]

Needs tests, CHANGELOG and possible README updates please.

[koenpunt]

I think the Content-Type should be application/hal+json as well, what do you think?

At least according to the spec: https://github.com/mikekelly/hal_specification/blob/master/hal_specification.md#how-to-serve-hal

[dblock]

You mean the default content-type? Yes.

[koenpunt]

I'll update the CHANGELOG in a bit

[koenpunt]

For now tagged it as 0.7.0-pre, but I think we can maybe combine this with #80. Because if we're going break the API we better break it good :)

[dblock]

This is good, would you mind rebasing and squashing your commits please?

[koenpunt]

Done, and what do you think of my suggestion in #80?

[dblock]

I did comment on #80, I would take the change, just needs README, CHANGELOG, tests, etc.

[koenpunt]

Yeah I know, I meant to wait with the release because it could break things.