Removed calls to deprecated node API.

Fixed warning message from Node: "http.createClient is deprecated. Use `http.request` instead."
Added Content-Length header to all requests, tests
Merge branch 'master' of https://github.com/postageapp/postageapp-nodejs

Conflicts:
	lib/postageapp.js
Merge pull request #9 from derek-watson/master

Added content-length header, tests