data: use lxml to get the XDG categories (#422)
data: use lxml to get the XDG categories (#422)

Use lxml to get the list of XDG categories from the DocBook file using
XPath queries; this simplifies the code a bit, and makes it more robust.

There is no change in the extracted data.
ximion/appstream,ximion/appstream,ximion/appstream,ximion/appstream