Show "assembling" when assembling

Merlin 32 is slow enough with a 64K data file that you have
enough time to read the text.

SourceGen/Properties/Resources.Designer.cs

@@ -753,6 +753,15 @@ namespace SourceGen.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Executing assembler....
+        /// </summary>
+        internal static string PROGRESS_ASSEMBLING {
+            get {
+                return ResourceManager.GetString("PROGRESS_ASSEMBLING", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Generating {0}....
         /// </summary>