Adding support for set_charset for mysqli and dio

This allows for multilingual support when updating and inserting using the Database Interface Object.

Note:
I did not implement the logic for the data_trans class because I'm not sure if we should use set_opt and get_opt? Also also, it appears it would have to be in the execute method and the data_query method.  Please confirm is this is the case and how you'd like to approach that.  For now at least it's working with the DIO.