Shared exchange functionality (#214)

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

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace CryptoExchange.Net.SharedApis
+{
+    /// <summary>
+    /// Client for request funding rate records
+    /// </summary>
+    public interface IFundingRateRestClient : ISharedClient
+    {
+        /// <summary>
+        /// Funding rate request options
+        /// </summary>
+        GetFundingRateHistoryOptions GetFundingRateHistoryOptions { get; }
+        /// <summary>
+        /// Get funding rate records
+        /// </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<SharedFundingRate>>> GetFundingRateHistoryAsync(GetFundingRateHistoryRequest request, INextPageToken? nextPageToken = null, CancellationToken ct = default);
+    }
+}