[tei-council] more Pure ODD

Lou -- I've just tweaked some of the discussion in USE.xml to reflect the new Pure ODD world order. (And also a dozen or so example <datatype>s that still used rng:ref.) You may want to take a look at the updated prose in 23.3.1.4 "Modification of Attribute and Attribute Value Lists". In particular, I used the noun phrase "Pure ODD", but I notice it is spelled "pure ODD" in ST. Thanks. I did this stuff in the 'dev' branch, f24618e.