Initial setup of XmlObjectModel to Serializable interface
Fixing recursive XmlObjectModel serialization on Serializable properties
Serializable now use nick for properties name. Fiexed segfault.
* serialized_property_use_blurb renamed to serialized_property_use_nick
* serialized_xml_node_value default to null
Implemented Serializable.deserialize()
* Added test case for serialize()
* Added SerializableObjectModel class to help Serializable implementators
Fixes to Serializable.deserialize()
* Moved string_to_gvalue to Serializable interface
* Serializable.serialize_property() deprecates use of ParamSpec
Fixing Serializable.serialize() and deserialize() on conplex Element nodes
Fixes on SerializableTest
Fixed serialization and Element.content property
SerializableObjectModel: removed value property
Added UML diagram documentation
Bugs and warnning messages fixes.
* Not used Serializable.serialized_xml_node removed
* Serializable.deserealize fixed return value
* Fixed a bug adding content to top level Element
* Removed warnnings
* Added SerializableError error domain
mplemented serialize non-automatic serializable properties
* Implementors must attach a handler to serialize_unknown_property
  event in order to serialize any property type non handled
  automatically like GLib.Array, GLib.HashTable or others
* Added serialized_node_name property to allow implementator to
  override default node name; default is GObject Type's name
* Removed warning messsages
Fixed (again) deserialize objects with objects as properties
Set type=xmlChar* on parametres, part 1
Set type=xmlChar* on parametres, part 2: those with string return types and other nearby changes
Set type=xmlChar* on fields
Set type=xmlChar* on method return values
Fix some cnames in libxml-2.0.vapi
Update libvala version; need a better solution to this
Add some TODO items for the future