Added request retry modes

src/Discord.Net.Core/RetryMode.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace Discord
+{
+    /// <summary> Specifies how a request should act in the case of an error. </summary>
+    [Flags]
+    public enum RetryMode
+    {
+        /// <summary> If a request fails, an exception is thrown immediately. </summary>
+        AlwaysFail = 0x0,
+        /// <summary> Retry if a request timed out. </summary>
+        RetryTimeouts = 0x1,
+        /// <summary> Retry if a request failed due to a network error. </summary>
+        RetryErrors = 0x2,
+        /// <summary> Retry if a request failed due to a ratelimit. </summary>
+        RetryRatelimit = 0x4,
+        /// <summary> Retry if a request failed due to an HTTP error 502. </summary>
+        Retry502 = 0x8,
+        /// <summary> Continuously retry a request until it times out, its cancel token is triggered, or the server responds with a non-502 error. </summary>
+        AlwaysRetry = RetryTimeouts | RetryErrors | RetryRatelimit | Retry502,
+    }
+}