= New Features

* An is_distinct_from extension has been added with support for the
  SQL IS DISTINCT FROM operator.  This operator is similar to the
  not equals operator, except in terms of NULL handling.  It returns
  true if only one side is NULL, and false if both sides are NULL.
  You can call is_distinct_from on Sequel itself or on Sequel objects:

    Sequel.is_distinct_from(:column_a, :column_b)
    Sequel[:column_a].is_distinct_from(:column_b)
    # (column_a IS DISTINCT FROM column_b)

  On databases not supporting IS DISTINCT FROM, support is emulated
  using a CASE statement.

* Column definitions on MySQL can use the :on_update_current_timestamp
  option for ON UPDATE CURRENT_TIMESTAMP, which creates a column that
  will automatically have its value set to CURRENT_TIMESTAMP on every
  update.

* Database#create_function on PostgreSQL now supports a :parallel
  option to set the thread safety of the funciton.  The value should
  be :safe, :unsafe, or :restricted.
