Add Pit file stability fee event

- file event on the pit contract is overloaded and each implementation
  logs a note
- existing Pit file transformer now specified as dealing with ilks

pkg/transformers/pit_file/debt_ceiling/debt_ceiling_suite_test.go

@@ -0,0 +1,13 @@
+package debt_ceiling_test
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+func TestDebtCeiling(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "DebtCeiling Suite")
+}