Change include path of mysql.h and errmsg.h to default path

[yurablok]

Please change the include path of mysql.h and errmsg.h from

#include <mysql/mysql.h>
#include <mysql/errmsg.h>

to

#include <mysql.h>
#include <errmsg.h>

since the default path for these files does not contain mysql.
For example:
"C:\Program Files\MySQL\MySQL Connector C 6.1\include\mysql.h"
"C:\Program Files\MySQL\MySQL Server 8.0\include\mysql.h"

With the extra mysql part of the path, I have to move the files to folder mysql or edit the path in mysql+++.h.