Implemented command type readers, parser and service.

src/Discord.Net.Commands/Results/ParseResult.cs

@@ -0,0 +1,35 @@
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace Discord.Commands
+{
+    [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
+    public struct ParseResult : IResult
+    {
+        public IReadOnlyList<object> Values { get; }
+
+        public CommandError? Error { get; }
+        public string ErrorReason { get; }
+
+        public bool IsSuccess => !Error.HasValue;
+
+        private ParseResult(IReadOnlyList<object> values, CommandError? error, string errorReason)
+        {
+            Values = values;
+            Error = error;
+            ErrorReason = errorReason;
+        }
+
+        internal static ParseResult FromSuccess(IReadOnlyList<object> values)
+            => new ParseResult(values, null, null);
+        internal static ParseResult FromError(CommandError error, string reason)
+            => new ParseResult(null, error, reason);
+        internal static ParseResult FromError(SearchResult result)
+            => new ParseResult(null, result.Error, result.ErrorReason);
+        internal static ParseResult FromError(TypeReaderResult result)
+            => new ParseResult(null, result.Error, result.ErrorReason);
+
+        public override string ToString() => IsSuccess ? "Success" : $"{Error}: {ErrorReason}";
+        private string DebuggerDisplay => IsSuccess ? $"Success ({Values.Count} Values)" : $"{Error}: {ErrorReason}";
+    }
+}