Separate interface and base_url for serve

You can now have a different base_url and listening interface.
The `gutenberg serve` cmd now accepts `-u`/`--base-url`, but it defaults to `127.0.0.1`.

It's either Arch Linux or archlinux but never Archlinux or ArchLinux.

From #191

* Finishing up site

* Make site a bit responsive

* Fix menu responsiveness

* Remove Fira Sans and revamp a bit text

* Update list of syntax and change output of syntax

* Add Rust mention

* Some doc tweaks

* Correct capitalization for GitHub

Correct capitalization for GitHub

* Some CSS tweaks

* More css tweaks + favicon

* Add link to my site

And some tweaks as I write the docs