Fix syntax errors in html files, apply dos2unix, prettier everything (#1244)

* Fix syntax errors in html files

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

examples/numpy_canvas_fractals.html

@@ -334,8 +334,8 @@ async def main():
   )
 
 asyncio.ensure_future(main())
-    </py-script>
+        </py-script>
+      </py-tutor>
    </section>
-  </py-tutor>
   </body>
 </html>