Add Autoload to Module Attribute

[UNTESTED] Adds an optional parameter to the Module attribute, "autoload", which defaults to true.

Specifies whether or not the assembly crawler should load this module.

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

@@ -6,13 +6,16 @@ namespace Discord.Commands
     public class ModuleAttribute : Attribute
     {
         public string Prefix { get; }
-        public ModuleAttribute()
+        public bool Autoload { get; }
+        public ModuleAttribute(bool autoload = true)
         {
             Prefix = null;
+            Autoload = autoload;
         }
-        public ModuleAttribute(string prefix)
+        public ModuleAttribute(string prefix, bool autoload = true)
         {
             Prefix = prefix;
+            Autoload = autoload;
         }
     }
 }