Supporting Unit.VALUE, to replace #()

#KT-2358 In Progress

runtime/src/jet/StringTemplate.java

@@ -58,7 +58,7 @@ public class StringTemplate {
             @Override
             public Tuple0 invoke(Object o) {
                 builder.append(o);
-                return Tuple0.INSTANCE;
+                return Tuple0.VALUE;
             }
         });
         return builder.toString();

runtime/src/jet/Tuple0.java

@@ -23,19 +23,19 @@ import org.jetbrains.jet.rt.annotation.AssertInvisibleInResolver;
  */
 @AssertInvisibleInResolver
 public class Tuple0 extends Tuple {
-    public static final Tuple0 INSTANCE = new Tuple0();
+    public static final Tuple0 VALUE = new Tuple0();
 
     private Tuple0() {
     }
 
     @Override
     public String toString() {
-        return "()";
+        return "Unit.VALUE";
     }
 
     @Override
     public boolean equals(Object o) {
-        return o == INSTANCE;
+        return o == VALUE;
     }
 
     @Override