Changed GetSrcLineNumber() and GetSrcLinePosition() extension methods to use the position info embedded within the srcML.
Added SrcMLElement.GetFileNameForUnit()
Merge remote-tracking branch 'remotes/origin/master' into topic-data-incrementalupdate
Added new SourceLocation class to centralize location data (xpath, file name, line number, and column).

All relevant classes now have a SourceLocation, and the parsers set it whenever possible.