Adding basic (but flexible) notification system which hooks into logrus.

This only adds e-mail notifications, but others could be easily done. In
many cases, adding another existing logrus hook will be sufficient.

notifications/notifier.go

@@ -0,0 +1,46 @@
+package notifications
+
+import (
+	log "github.com/Sirupsen/logrus"
+	"github.com/urfave/cli"
+)
+
+type typeNotifier interface {
+	StartNotification()
+	SendNotification()
+}
+
+type Notifier struct {
+	types []typeNotifier
+}
+
+func NewNotifier(c *cli.Context) *Notifier {
+	n := &Notifier{}
+
+	// Parse types and create notifiers.
+	types := c.GlobalStringSlice("notifications")
+	for _, t := range types {
+		var tn typeNotifier
+		switch t {
+		case emailType:
+			tn = newEmailNotifier(c)
+		default:
+			log.Fatalf("Unknown notification type %q", t)
+		}
+		n.types = append(n.types, tn)
+	}
+
+	return n
+}
+
+func (n *Notifier) StartNotification() {
+	for _, t := range n.types {
+		t.StartNotification()
+	}
+}
+
+func (n *Notifier) SendNotification() {
+	for _, t := range n.types {
+		t.SendNotification()
+	}
+}