redirect /page to /page.html

[Anton-4]

Thanks for working on simple-http-server, it's been working great for us!

We use simple-http-server for local development on our website, one issue we have is that our links are set up like /tutorial not /tutorial.html. This currently results in a 404.

Would you accept a pull request that adds this functionality?

[Anton-4]

I implemented this in my fork https://github.com/Anton-4/simple-http-server