TODO doc for Atk namespace.

There are in total 66 xml to document in Atk. Right now there are 66 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:

Action.xml
ActiveDescendantChangedArgs.xml
ActiveDescendantChangedHandler.xml
Attribute.xml
ChildrenChangedArgs.xml
ChildrenChangedHandler.xml
ColumnDeletedArgs.xml
ColumnDeletedHandler.xml
ColumnInsertedArgs.xml
ColumnInsertedHandler.xml
Component.xml
CoordType.xml
Document.xml
EditableText.xml
EventListener.xml
EventListenerInit.xml
Focus.xml
FocusEventArgs.xml
FocusEventHandler.xml
FocusHandler.xml
Function.xml
GObjectAccessible.xml
Global.xml
Hyperlink.xml
HyperlinkStateFlags.xml
Hypertext.xml
Image.xml
Implementor.xml
KeyEventStruct.xml
KeyEventType.xml
KeySnoopFunc.xml
Layer.xml
NoOpObject.xml
NoOpObjectFactory.xml
Object.xml
ObjectFactory.xml
PropertyChangeArgs.xml
PropertyChangeEventHandler.xml
PropertyChangeHandler.xml
PropertyValues.xml
Registry.xml
Relation.xml
RelationSet.xml
RelationType.xml
Role.xml
RowDeletedArgs.xml
RowDeletedHandler.xml
RowInsertedArgs.xml
RowInsertedHandler.xml
Selection.xml
StateChangeArgs.xml
StateChangeHandler.xml
StateManager.xml
StateSet.xml
StateType.xml
StreamableContent.xml
Table.xml
Text.xml
TextAttribute.xml
TextBoundary.xml
TextCaretMovedArgs.xml
TextCaretMovedHandler.xml
TextChangedArgs.xml
TextChangedHandler.xml
Util.xml
Value.xml