Add support for repeated timestamps and durations to to_dict from_dict (#211)

tests/inputs/repeated_duration_timestamp/repeated_duration_timestamp.proto

@@ -0,0 +1,10 @@
+syntax = "proto3";
+
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+
+
+message Test {
+    repeated google.protobuf.Timestamp times = 1;
+    repeated google.protobuf.Duration durations = 2;
+}