0.2.0

Add new ValueObject class

A class extending a ValueObject class should define its properties as
"public readonly" (on PHP8.1+) or "protected" (on PHP8.0) on the constructor.

ValueObject objects are immutable. Private or public properties can be accessed
like public properties or array indexes. Readonlyness in PHP8.0 is achieved
by implementing a magic __set() method.

0.1.1

Added return types for PHP 8.1

0.1

Message for disabled test