Optional generation of extension (R.xx)

Optional generation of Colors/Fonts/Images/Stringium extension

Sources/ResgenSwift/Generate/Runnable/StringsConfiguration+Runnable.swift

@@ -24,26 +24,24 @@ extension StringsConfiguration: Runnable {
             langs,
             "--default-lang",
             defaultLang,
-            "--extension-output-path",
-            extensionOutputPath.prependIfRelativePath(projectDirectory),
             "--static-members",
             "\(staticMembersOptions)",
             "--xc-strings",
             "\(xcStringsOptions)"
         ]
 
-        if let extensionName {
-            args += [
-                "--extension-name",
-                extensionName
-            ]
-        }
-
-        if let extensionSuffix {
-            args += [
-                "--extension-suffix",
-                extensionSuffix
-            ]
+        // Add optional parameters
+        [
+            ("--extension-output-path", extensionOutputPath?.prependIfRelativePath(projectDirectory)),
+            ("--extension-name", extensionName),
+            ("--extension-suffix", extensionSuffix)
+        ].forEach { argumentName, argumentValue in
+            if let argumentValue {
+                args += [
+                    argumentName,
+                    argumentValue
+                ]
+            }
         }
 
         Stringium.main(args)