Generate XML tree

The module sphinx_doxysummary.xmltree is used to create a map from item names to their corresponding Doxygen descriptions. The result is saved to the module variable xml_tree, which is called when Sphinx parses rst files. When the summary table is constructed, summaries of the items are retrieved from their Doxygen descriptions stored in the variable.

Note that because function overloading is allowed in C++, the generated map is one-to-many (i.e. a name is mapped to a list of all possible descriptions sharing the same name).

DoxygenItem	Item read from Doxygen generated xml.
process_generate_xmltree	Create a tree of name -> DoxygenItem.
xml_tree	Map of item names to a list of corresponding DoxygenItem objects.