Improve overview of modified pages

WebsiteGenerator/Files/FileSystem.swift

@@ -76,6 +76,11 @@ final class FileSystem {
      */
     private var imageTasks: [String : ImageOutput] = [:]
 
+    /**
+     The paths to all pages which were changed
+     */
+    private var generatedPages: Set<String> = []
+
     init(in input: URL, to output: URL) {
         self.input = input
         self.output = output
@@ -474,6 +479,21 @@ final class FileSystem {
         pagePaths[id]
     }
 
+    func generated(page: String) {
+        generatedPages.insert(page)
+    }
+
+    func printGeneratedPages() {
+        guard !generatedPages.isEmpty else {
+            print("No pages modified")
+            return
+        }
+        print("\(generatedPages.count) pages modified")
+        for page in generatedPages.sorted() {
+            print("  " + page)
+        }
+    }
+
 
     // MARK: Writing files