Support serving extensionless HTML pages

[omentic]

The live Hakyll server is helpful and behaves exactly as one would expect it to. But one thing that static site hosts ex. Github Pages, Neocities often do is serve a file **/foo.html at both **/foo.html and **/foo: as the .html is usually redundant.

It would be nice for the default Hakyll server to support this. I believe there's a way to add this functionality in, but it would be convenient to have direct support so that a site that uses .html-less links can be navigable with the included server.

[Minoru]

I think we could add the linked helper function into Hakyll (if the code's author is ok with this), but I'd be against enabling this by default. Nginx, Apache, and even the new-fangled Caddy require manually configuring this. Are you aware of any semi-popular webservers that do this by default? Tying our default config to a specific host isn't something that I'd be in favour of doing.

[omentic]

I'm not aware of any webservers that do it by default, no: just the hosts themselves (though most hosts seem to do so).

It would be really cool if it could be a flag to site watch! Not changing the default config makes sense.