Add checker class to check if generation of font are required + Split CLIToolCore in multiple file (one by class)

Sources/CLIToolCore/GeneratorChecker.swift

@@ -0,0 +1,40 @@
+//
+//  GeneratorChecker.swift
+//  
+//
+//  Created by Thibaut Schmitt on 22/12/2021.
+//
+
+import Foundation
+
+public class GeneratorChecker {
+    
+    /// Return `true` if  inputFile is newer than extensionFile, otherwise `false`
+    public static func shouldGenerate(force: Bool, inputFilePath: String, extensionFilePath: String) -> Bool {
+        guard force == false else {
+            return true
+        }
+        
+        // If inputFile is newer that generated extension -> Regenerate
+        let extensionFileURL = URL(fileURLWithPath: extensionFilePath)
+        let inputFileURL = URL(fileURLWithPath: inputFilePath)
+        
+        let extensionRessourceValues = try? extensionFileURL.resourceValues(forKeys: [URLResourceKey.contentModificationDateKey])
+        let inputFileRessourceValues = try? inputFileURL.resourceValues(forKeys: [URLResourceKey.contentModificationDateKey])
+        
+        if let extensionModificationDate = extensionRessourceValues?.contentModificationDate,
+           let inputFileModificationDate = inputFileRessourceValues?.contentModificationDate {
+            if inputFileModificationDate >= extensionModificationDate {
+                print("Input file is newer that generated extension.")
+                return true
+            } else {
+                return false
+            }
+        }
+    
+        // ModificationDate not available for both file
+        print("⚠️ Could not compare file modication date. ⚠️")
+        return true
+    }
+    
+}