Shared exchange functionality (#214)

CryptoExchange.Net/SharedApis/Interfaces/Rest/Futures/IMarkPriceKlineRestClient.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace CryptoExchange.Net.SharedApis
+{
+    /// <summary>
+    /// Client for getting the mark price klines for a symbol
+    /// </summary>
+    public interface IMarkPriceKlineRestClient : ISharedClient
+    {
+        /// <summary>
+        /// Mark price klines request options
+        /// </summary>
+        GetKlinesOptions GetMarkPriceKlinesOptions { get; }
+        /// <summary>
+        /// Get mark price kline/candlestick data
+        /// </summary>
+        /// <param name="request">Request info</param>
+        /// <param name="nextPageToken">The pagination token from the previous request to continue pagination</param>
+        /// <param name="ct">Cancellation token</param>
+        Task<ExchangeWebResult<IEnumerable<SharedFuturesKline>>> GetMarkPriceKlinesAsync(GetKlinesRequest request, INextPageToken? nextPageToken = null, CancellationToken ct = default);
+    }
+}