Add documentation for new $options parameter in dba::delete
*
* @param string $table Table name
* @param array $conditions Field condition(s)
+ * @param array $options
+ * - cascade: If true we delete records in other tables that depend on the one we're deleting through
+ * relations (default: true)
* @param boolean $in_process Internal use: Only do a commit after the last delete
* @param array $callstack Internal use: prevent endless loops
*