Make TypeAlias.getValue() public again

Another revert from 0.3.0. TypeAlias is not meant to be monadic in any form.
It is a simple alias for another (non-generic) type.

src/main/java/net/kemitix/mon/TypeAlias.java

@@ -87,7 +87,7 @@ public abstract class TypeAlias<T> {
      *
      * @return the value
      */
-    private T getValue() {
+    public T getValue() {
         return value;
     }
 }