Simple notification framework (#297)

* bonfire notifications working

* make interface to make more extensible

* some docs

* typo

* rename typo

pkg/notifications/notifications.go

@@ -0,0 +1,41 @@
+package notifications
+
+// Notifier is a type that can send a notification
+type Notifier interface {
+	// Notify will be called after a correction is performed.
+	// It will be given the correction's message, the result of executing it,
+	// and a flag for whether this is a preview or if it actually ran.
+	// If preview is true, err will always be nil.
+	Notify(domain, provider string, message string, err error, preview bool)
+	// Done will be called exactly once after all notifications are done. This will allow "batched" notifiers to flush and send
+	Done()
+}
+
+// new notification types should add themselves to this array
+var initers = []func(map[string]string) Notifier{}
+
+// Init will take the given config map (from creds.json notifications key) and create a single Notifier with
+// all notifications it has full config for.
+func Init(config map[string]string) Notifier {
+	notifiers := multiNotifier{}
+	for _, i := range initers {
+		n := i(config)
+		if n != nil {
+			notifiers = append(notifiers, n)
+		}
+	}
+	return notifiers
+}
+
+type multiNotifier []Notifier
+
+func (m multiNotifier) Notify(domain, provider string, message string, err error, preview bool) {
+	for _, n := range m {
+		n.Notify(domain, provider, message, err, preview)
+	}
+}
+func (m multiNotifier) Done() {
+	for _, n := range m {
+		n.Done()
+	}
+}