Parameter preconditions and typereader overriding

src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Discord.Commands
+{
+    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = true, Inherited = true)]
+    public abstract class ParameterPreconditionAttribute : Attribute
+    {
+        public abstract Task<PreconditionResult> CheckPermissions(CommandContext context, ParameterInfo parameter, object value);
+    }
+}