make the json object ordered

[johnscancella]

If you use a linkedHashMap instead of just hashMap you can easily make it ordered. I work on https://github.com/LibraryOfCongress/bagger which needs the JSONObject to preserve the ordering of the fields.

[erosb]

The object ordering has already been discussed in #190 and has been rejected for 2 reasons:

• the json specification says that objects are unordered, and this library shouldn't go against it
• switching to LinkedHashMap would cause serious performance problems for larger objects, since the lookup (JSONObject.opt(key)) is expensive

[stleary]

Thanks, but can't accept this change. If you really need ordered JSONObjects, you might want to fork the project. A Library of Congress project sounds pretty cool, good luck!