Post json within request body

This is a feature request, and I think it's raised in #531 but misunderstanded

Description:

Now only form data format is supported in this plugin, I'd like to post json data in post body (like this: https://stackoverflow.com/questions/5570747/jquery-posting-json)

In jquery it can be done with code below:

$.ajax(url, {
    data : JSON.stringify(myJSObject),
    contentType : 'application/json',
    type : 'POST',
    ...

Expected Behavior:

With option:

contentType : 'application/json',

Request body like this :

{"name":"apple","count":"1"}

Actual behavior:

Unsupported, now only encoded form data can be in post body
Request body like this:

name=apple&count=1

Why

It's quite common in now days for communicating with server in protocol of json instead of form data, so this feature is needed.

The issue names no file or test; start by locating the plugin's request serialization and contentType handling. Verify that application/json produces the stated JSON body while existing form-encoded submission remains unchanged.