Update YAXSerializer.cs

Added the possibility to ignore to serialize yaxlib namespace, and also yaxlib:realtype attribute.
This attribute is no longer needed if you have the meta information set on your .net model.

"Feature" can be used by invoking the yaxlib constructor with a certain parameter: e.g.
 Dim lSerializer = New YAXSerializer(GetType(RnDSuiteFile), True)
(Yes... :) I am using vb.net)