Completed XEP-0157 and XEP-0203

I've published the first results of my GSoC project.

The task consisted on adding or updating support for two protocols on ejabberd:
XEP-0157: Contact Addresses for XMPP Services
XEP-0203: Delayed Delivery

The objective of this task was to get some experience reading XEPs. The coding part was easy, since both protocols were rather small and easy to implement. So, I decided to update also some related code.

More info and patch downloads: XEP-0157 and XEP-0203.

The plan is to commit those patches to ejabberd SVN soon, even before GSoC finishes. I hope there aren't bugs. Otherwise, please comment it here or on the bug tracker.