Binance: implement get historic trades (#588)

* Binance: implement get historic trades

* get binance trade data based on aggregate trade list
* fix small issue in rpc server: gctcli stops retrieving when there's
a gap in data

* update binance trade history availability in readme

* limit check batched aggregate requests

* add test for batched aggregated trades
* fix batch fromId query parameter
* update documentation

* send a serialised currency pair to GetAggregatedTrades

the rationale is that the API is kept generic so that callers can shoot
themselves in the foot if they want to

* allow requesting arbitrary limit of trades

* handle some error cases for batching GetAggregateTrades

* fix batch without end time

* don't return from batch too early if end time is not set
* additional check for supported limits

* don't use CheckLimits for GetAggregatedTrades

* the exchange doesn't use predefined valid limits for this request

engine/rpcserver.go

@@ -2793,13 +2793,16 @@ func (s *RPCServer) GetHistoricTrades(r *gctrpc.GetSavedTradesRequest, stream gc
 		Asset:        r.AssetType,
 		Pair:         r.Pair,
 	}
-	iterateStartTime := UTCStartTime
-	iterateEndTime := iterateStartTime.Add(time.Hour)
-	for iterateStartTime.Before(UTCEndTime) {
+
+	for iterateStartTime := UTCStartTime; iterateStartTime.Before(UTCEndTime); iterateStartTime = iterateStartTime.Add(time.Hour) {
+		iterateEndTime := iterateStartTime.Add(time.Hour)
 		trades, err = exch.GetHistoricTrades(cp, asset.Item(r.AssetType), iterateStartTime, iterateEndTime)
 		if err != nil {
 			return err
 		}
+		if len(trades) == 0 {
+			continue
+		}
 		grpcTrades := &gctrpc.SavedTradesResponse{
 			ExchangeName: r.Exchange,
 			Asset:        r.AssetType,
@@ -2820,8 +2823,6 @@ func (s *RPCServer) GetHistoricTrades(r *gctrpc.GetSavedTradesRequest, stream gc
 		}
 
 		stream.Send(grpcTrades)
-		iterateStartTime = iterateStartTime.Add(time.Hour)
-		iterateEndTime = iterateEndTime.Add(time.Hour)
 	}
 	stream.Send(resp)