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

test/empty-block_test.go

@@ -0,0 +1,12 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/rule"
+)
+
+// TestEmptyBlock rule.
+func TestEmptyBlock(t *testing.T) {
+	testRule(t, "empty-block", &rule.EmptyBlockRule{})
+}