Add VelocityLanguageDriverConfig like as mybatis-thymeleaf 

Configuration class is friendly to spring boot configuration properties.

### Specifications

In this change, add the `VelocityLanguageDriverConfig` and add a new constructor on the `VelocityLanguageDriver` for passing it. For details, refer to #72.

### About backward compatibility

This change keep the backward compatibility.

### Related Issues

* mybatis/freemarker-scripting#44