RFC: Support of REPLACE INTO

[vanjohnnl]

The function insert_update does not work with multiple rows. Could you add the support of the SQL statement REPLACE INTO to your class?

I have now duplicated the insert and multi_insert-function, renamed it to (multi_)replace and changed the query within $sql to:

$sql = "REPLACE INTO `{$table}`

This is working for me, but I would lose it when installing a new release.

[mrcrypster]

Added replace() and multi_replace() methods.