More meaningful toString() method

Produce toString without dilligently adding it to every single class.
Rely on heuristics to cut down the number of fields to show.

src/main/java/org/kohsuke/github/SkipFromToString.java

@@ -0,0 +1,16 @@
+package org.kohsuke.github;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Ignores this field for {@link GHObject#toString()}
+ *
+ * @author Kohsuke Kawaguchi
+ */
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+@interface SkipFromToString {
+}