Fix CryptoUtility.PrecisionToStepSize and add rate limit for Poloniex (#800)

* [Poloniex] Remove ExchangeGlobalCurrencyReplacements entry

* [Poloniex] Add rate limit

* Fix CryptoUtility.PrecisionToStepSize

Author: BZ-CO

src/ExchangeSharp/API/Exchanges/Poloniex/ExchangePoloniexAPI.cs

@@ -33,6 +33,7 @@ private ExchangePoloniexAPI()
 			RequestContentType = "application/json";
 			MarketSymbolSeparator = "_";
 			WebSocketOrderBookType = WebSocketOrderBookType.DeltasOnly;
+			RateLimit = new RateGate(10, TimeSpan.FromSeconds(1));
 		}
 
 		/// <summary>
@@ -78,9 +79,8 @@ protected override Task OnInitializeAsync()
 					fieldCount[split[0]] = split[1].ConvertInvariant<int>();
 				}
 			}
-
 			WithdrawalFieldCount = fieldCount;
-			ExchangeGlobalCurrencyReplacements["STR"] = "XLM"; // wtf
+
 			return Task.CompletedTask;
 		}
 

src/ExchangeSharp/Utility/CryptoUtility.cs

@@ -1412,14 +1412,12 @@ public static decimal CalculatePrecision(string numberWithDecimals)
         /// </summary>
         public static decimal PrecisionToStepSize(decimal precision)
         {
+	        if (precision == 0) return 1;
+
 	        var sb = new StringBuilder();
 	        sb.Append("0");
 	        if (precision > 0) sb.Append(".");
-	        if (precision == 1)
-	        {
-		        sb.Append("1");
-		        return decimal.Parse(sb.ToStringInvariant());
-	        }
+
 	        for (var i = 0; i < precision; i++)
 	        {
 		        sb.Append(i + 1 == precision ? "1" : "0");