of unicode situations that occur in db's such as MS-SQL to be
better handled and allows subclassing of the Unicode datatype.
[ticket:522]
+ - ClauseElements can be used in in_() clauses now, such as bind
+ parameters, etc. #476
+ - reverse operators implemented for `CompareMixin` elements,
+ allows expressions like "5 + somecolumn" etc. #474
- the "where" criterion of an update() and delete() now correlates
embedded select() statements against the table being updated or
deleted. this works the same as nested select() statement