Add PostProcess annotation

configlib-core/src/main/java/de/exlll/configlib/PostProcess.java

@@ -0,0 +1,29 @@
+package de.exlll.configlib;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates that the annotated element should be post-processed. This
+ * annotation can be applied to fields and methods.
+ * <p>
+ * Applying this annotation to a field of a configuration class does not cause
+ * any post-processing to be triggered automatically. However, both, the
+ * presence of this annotation and the return value of its {@link #key()}
+ * method can be used as a filter criterion when adding post-processors via a
+ * {@code ConfigurationProperties} object.
+ * <p>
+ * When applied to a (non-static) method of a configuration type, the method is
+ * called immediately after a configuration instance of that type has been
+ * initialized. If the return type of the annotated method equals the
+ * configuration type, the instance is replaced by the return value of that
+ * method call. If the return type is {@code void}, then the method is simply
+ * called on the given instance.
+ */
+@Target({ElementType.FIELD, ElementType.METHOD})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface PostProcess {
+    String key() default "";
+}