Subtracter Single Method
Geoffrey Challen // 2021.2.0
Create a public class called Subtracter.
Subtracter should store a single int in a private field and provide a public setValue method
that sets the stored int to the passed value.
(You can initialize the stored value to 0.)
It should also provide a public method called subtract.
subtract should accept an int parameter, subtract it from the stored value, and return the updated value.
Do not implement getValue.