Simple MySQL handler: Execute SQL queries with MySQLi or MySQL extension

This is a simple class that can execute SQL queries with MySQLi or MySQL extension.

It can connect to a given MySQL server using the MySQLi extension if it is available or falls back to the old MySQL extension otherwise.

The class can execute common SQL queries to:

- Retrieve a single table field value
- Retrieve a single row
- Select all fields from a table that match a condition
- Select a field of a table that matches a condition
- Get a table column names
- Insert one or multiple records in table
- Update values of records that match a condition
- Lock or unlock tables