Adds new rule empty-block (#14)

* Adds rule superfluous-else (an extension of indent-error-flow)

* initial (non functional) version

* empty-block working version

* adds tests for empty-block rule

* Adds empty-block to the rules table

* code clean-up

fixtures/empty-block.go

@@ -0,0 +1,33 @@
+// Test of empty-blocks.
+
+package fixtures
+
+func f(x int) bool { // MATCH /this block is empty, you can remove it/
+
+}
+
+func g(f func() bool) string {
+	{ // MATCH /this block is empty, you can remove it/
+	}
+
+	if ok := f(); ok { // MATCH /this block is empty, you can remove it/
+		// only a comment
+	} else {
+		println("it's NOT empty!")
+	}
+
+	if ok := f(); ok {
+		println("it's NOT empty!")
+	} else { // MATCH /this block is empty, you can remove it/
+
+	}
+
+	for i := 0; i < 10; i++ { // MATCH /this block is empty, you can remove it/
+
+	}
+
+	for { // MATCH /this block is empty, you can remove it/
+
+	}
+
+}