`Ord` instance for `InternedText`

The `Ord` instance for `InternedText` compares identifiers rather than the underlying text. Presumably this is for efficiency, and is an entirely reasonable choice. However, I definitely think this behavior should be documented, since it is not obvious that a textual datatype will have anything other than the usual lexicographic sort order. People using `InternedText` are, in general, going to treat it as a drop-in hash-consed replacement for `Text`, unless there is documentation to the contrary.