feature: updated folder structure

- moved files into folders to match their current namespace
- did not update any namespaces to maintain backward compatibility

src/PepperDash.Essentials.Core/File/FileEventArgs.cs

@@ -0,0 +1,9 @@
+namespace PepperDash.Essentials.Core
+{
+    public class FileEventArgs
+    {
+        public FileEventArgs(string data) { Data = data; }
+        public string Data { get; private set; } // readonly
+
+    }
+}

src/PepperDash.Essentials.Core/File/FileIO.cs

@@ -269,10 +269,4 @@ namespace PepperDash.Essentials.Core
 		}
 
 	}
-	public class FileEventArgs
-	{
-		public FileEventArgs(string data) { Data = data; }
-		public string Data { get; private set; } // readonly
-
-	}
 }