XMLParser is now a singleton that stores a map of <filename, <document, document data> > pairs.

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Added methods are:

setCurDocument(string) - tells the parser which file to read from. This is automatically
set after a parse, but otherwise needs to be called prior to pulling data from the parser.

removeDocument(string) - the parser attempts to remove the specified filename from its document map.
This is mostly used be a few singleton classes that only use the parser to read in their initialization data.