revert to VB and update to new project file format

Pilz.Drawing/BitmapExtensions.vb

@@ -0,0 +1,20 @@
+Imports System.Drawing
+Imports System.Runtime.CompilerServices
+
+Public Module BitmapExtensions
+
+    <Extension>
+    Public Sub InvertColors(bmp As Bitmap)
+        For y As Integer = 0 To bmp.Height - 1
+            For x As Integer = 0 To bmp.Width - 1
+                Dim inv As Color = bmp.GetPixel(x, y)
+                inv = Color.FromArgb(inv.A,
+                                     Byte.MaxValue - inv.R,
+                                     Byte.MaxValue - inv.G,
+                                     Byte.MaxValue - inv.B)
+                bmp.SetPixel(x, y, inv)
+            Next
+        Next
+    End Sub
+
+End Module