Change namespace to Jackett.Common (#2691)

Really hope I don't break anything with this
Went to have a go at .NET core and it just became too confusing for me with 'Jackett' namespace referring to both Jackett.Common and Jackett

src/CurlSharp/CurlSlist.cs

@@ -20,6 +20,7 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
+using CurlSharp.Enums;
 
 namespace CurlSharp
 {