Add ability to configure response type in Ajax calls.

[matthughes]

No description provided.

[sjrd]

Review by @lihaoyi
ASAICT, this is OK. But I've never actually used this API, so I'm not the best judge.

[lihaoyi]

Could you say something about what this is useful for? I've never used this API either =P

[matthughes]

It changes the type of the 'xhr.response' field. By default, this is "", so response == responseText. (https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest#responseType)

Ajax.get("foo.json", responseType="json").map { xhr => xhr.response // response is JSON here, no need to call JSON.parse }

Ajax.get("foo.xml", responseType="document").map { xhr => xhr.response // response is Document here, no need to parse again }

[lihaoyi]

Looks good to me then