some initial sample code to try out PHP XML serialization
introducing XML support to the PHP classes
fixup the model update

Conflicts:

	src/Gedcomx/Agent/Agent.php
	src/Gedcomx/Conclusion/Subject.php
	src/Gedcomx/Source/SourceDescription.php
adding a brief XML serialization test
XML support fixes
fixup the model update

Conflicts:

	src/Gedcomx/Agent/Agent.php
	src/Gedcomx/Conclusion/Subject.php
	src/Gedcomx/Source/SourceDescription.php
test fixes