async_db_exec() - executes an sql statement then executes a callback

void async_db_exec( int handle, string sql_query, function callback );

This function will execute the passed sql statement for the given data‐
base handle.

Returns the database handle to the callback function provided.

The callback should follow this format:

    function (int handle) {
        db_close(handle);
    }

db_commit(3), db_exec(3), db_fetch(3), db_rollback(3), valid_database(4)