TODO doc for GConf namespace.

There are in total 7 xml to document in GConf. Right now there are 6 xml not documented in any proportion.
The idea is to have a easy way to know what documentation is missing, if you want to help or are helping please take out the xml that you commit
from the missing list. For documentation that take some time to finish (like HTML, TextBuffer, etc) the best is that you but your name and email
next to the file in this list to acknowledge that you are working in it (is recommendable that you suscribe to the mono-docs  mailing list).

Following is the list of undocumented xml:

ChangeSet.xml
Client.xml
NoSuchKeyException.xml
NotifyEventArgs.xml
NotifyEventHandler.xml
NotifyFuncNative.xml