Made .md extension optional

src/articles/cheat-sheets/index.md

@@ -5,4 +5,4 @@ If you add an `index.md` into a directory, it will become a part of the breadcru
 
 Use it as overview for subpages of that directory:
 
-- [Markdown cheat sheet](cheat-sheets/Markdown_cheat_sheet.md) - shows the markdown syntax.
+- [Markdown cheat sheet](cheat-sheets/Markdown_cheat_sheet) - shows the markdown syntax.

src/articles/index.md

@@ -7,4 +7,6 @@ Place the content of your *slim wiki* into this directory. Write it using
 Use the main page as overview and add links to subpages:
 
 - [Cheat Sheets](cheat-sheets) - You can add links to directories having a `index.md`.
-- [Markdown cheat sheet](cheat-sheets/Markdown_cheat_sheet.md) - Or add direct a link to a markdown file.
+- [Markdown cheat sheet](cheat-sheets/Markdown_cheat_sheet) - Or add direct a link to a markdown file.
+
+**Note:** The `.md` extension is optional when linking to markdown files.

src/server/logic/Main.php

@@ -12,10 +12,16 @@ class Main {
         $articleBaseDir = realpath(__DIR__ . '/../../articles') . '/';
         $articleFilename = $articleBaseDir . implode('/', $requestPathArray);
 
+        // Support `index.md` for directories
         if (is_dir($articleFilename)) {
             $articleFilename = rtrim($articleFilename, '/') . '/index.md';
         }
 
+        // Make the extension `.md` optional
+        if (! file_exists($articleFilename) && file_exists($articleFilename . '.md')) {
+            $articleFilename .= '.md';
+        }
+
         if (($articleFilename == realpath($articleFilename)) && file_exists($articleFilename) && is_readable($articleFilename)) {
             $wikiName = 'Slim Wiki'; // TODO: Make this configurable