fully convert redis over to custom key value store type

src/session/session_store.go

@@ -1,6 +1,14 @@
 package session
 
-import "time"
+import (
+	"errors"
+	"time"
+)
+
+var ErrSessionNotFound = errors.New("Session not found")
+var ErrSessionAlreadyExists = errors.New("Session already exists")
+var ErrSessionExpired = errors.New("Session expired")
+var ErrSessionBackend = errors.New("Session backend")
 
 type SessionData struct {
 	UserID    string    `json:"userid"`