Add doc on request notifications that are considered fatal

Part of sociomantic-tsunami#155.

src/dhtproto/client/request/Exists.d

@@ -46,6 +46,12 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * wrong_node
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/Get.d

@@ -67,6 +67,12 @@ public struct Timeout
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * wrong_node
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/GetAll.d

@@ -58,6 +58,11 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/GetChannels.d

@@ -35,6 +35,11 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/Mirror.d

@@ -85,6 +85,11 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/Put.d

@@ -67,6 +67,13 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * wrong_node
+    * value_too_big
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/Remove.d

@@ -53,6 +53,12 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * wrong_node
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/RemoveChannel.d

@@ -36,6 +36,12 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * not_permitted
+
 *******************************************************************************/
 
 private union NotificationUnion

src/dhtproto/client/request/Update.d

@@ -64,6 +64,12 @@ public struct Args
 
     Union of possible notifications.
 
+    The following notifications are considered fatal (i.e. the request will
+    almost certainly get the same error if retried):
+    * node_error
+    * unsupported
+    * wrong_node
+
 *******************************************************************************/
 
 private union NotificationUnion