= Improvements

* Dataset#empty? now correctly handles datasets using custom SQL or
  Dataset#values where the first value in the first row is NULL.

* Dataset#count without an argument or block now works correctly on
  Microsoft SQL Server when using custom SQL that uses ORDER BY.

* Dataset#count now works correctly for datasets using Dataset#values.

* Sequel now recognizes an additional SQLite constraint violation
  error that occurs with recent versions of amalgalite.

* Dataset#values will now raise an exception when called with an empty
  array. Previously, an exception would not be raised until the query
  was sent to the database.

= Backwards Compatibility

* The changes to make Dataset#empty? and #count work with custom SQL
  on Microsoft SQL Server now result in running the custom SQL, which
  could result in worse performance than in previous versions. You can
  wrap such datasets with Dataset#from_self manually to restore the
  previous behavior.
