Served pages should not require .html extension

[The-Noah]

Is your feature request related to a problem? Please describe.
It is quite common for pages to not require the .html extension when visiting them. The serve command should respect this.

Describe the solution you'd like
When using the built-in serve command, pages should be accessible without .html.

Additional context
A page called aboutme should be accessible from both aboutme.html and aboutme.

This can be found here and here.

Bonus if pages are also accessible from the .htm extension.