doc/rfc: v3 api supports for consistent range request

Documentation/rfc/v3api.md

@@ -94,8 +94,9 @@ message ResponseHeader {
   optional string error = 1;
   optional uint64 cluster_id = 2;
   optional uint64 member_id = 3;
-  // index of the store when the requested was processed.
+  // index of the store when the request was applied.
   optional int64 index = 4;
+  // term of raft when the request was applied.
   optional uint64 raft_term = 5;
 }
 
@@ -105,12 +106,22 @@ message RangeRequest {
   // if the end_key is given, it gets the keys in range [key, end_key).
   optional bytes end_key = 2;
   // limit the number of keys returned.
+  // if not all the keys are returned, a continue id will be 
+  // returned in the range response.
   optional int64 limit = 3;
+  // continue the previous range request in a consistent
+  // manner if a continue id is provided.
+  optional int64 continue_id = 4;
 }
 
 message RangeResponse {
   optional ResponseHeader header = 1;
   repeated KeyValue kvs = 2;
+  optional continue_id = 3;
+  // the next range request with continue_id must
+  // be issued with in continue_timeout to the
+  // same server.
+  optional continue_timeout = 4;
 }
 
 message PutRequest {
@@ -239,6 +250,9 @@ message Action {
     expire = 2;
   }
   optional ActionType event_type = 1;
+  // a put action contains the put key-value
+  // a delete/expire action contains the previous
+  // key-value
   optional KeyValue kv = 2;
 }