Ensure the correct order of files and the TOC.

src/book.cpp

@@ -58,7 +58,7 @@ book read(const fs::path filepath, const bool raw)
         {
             doc.text_raw = zip::read_file(filepath, entry);
         }
-        current_book.files.insert({entry, doc});
+        current_book.files.emplace_back(entry, doc);
     }
 
     return current_book;

src/book.hpp

@@ -22,6 +22,8 @@
 #include <map>
 #include <string>
 #include <string_view>
+#include <utility>
+#include <vector>
 
 namespace epubgrep::book
 {
@@ -41,8 +43,8 @@ struct document
 //! EPUB file.
 struct book
 {
-    std::map<string, document> files; //!< filename, file
-    std::map<string, string> toc;     //!< title, href
+    std::vector<std::pair<string, document>> files; //!< filename, file
+    std::vector<std::pair<string, string>> toc;     //!< title, href
     string language;                                //!< Book language
 } __attribute__((aligned(128)));