GitLab

ENH: Add XdmfGeometryType to XdmfGeometry in a similar implementation as XdmfTopologyType.  Add tests for XdmfGeometry.  Add XdmfItem, an abstract class that is able to be traversed by an XdmfVisitor to write out its information to XML and HDF5 or other heavy data formats.  Modify XdmfGeometry, XdmfGrid, XdmfTopology, and XdmfAttribute to inherit from XdmfItem.

ENH: Added XdmfTopologyType to XdmfTopology to handle element types and associated const data like nodesPerElement and name.  This resembles "Replace subclass with fields" implementation in Refactoring and does a nice job encapsulating element type data in an enum like way avoiding unneccesary subclassing.