Add new server.open option and --open CLI flag

[valtlai]

Works on MacOS, but should be tested on Linux and Windows too.

[oscarotero]

Thanks!
In windows, the command works fine. I couldn't test it in linux but have seen xdg-open <url> in other implementations like this or this. I'm going to ask to a friend with linux to test it, and if it works fine, I'll merge it.

[valtlai]

I switched it to xdg-open because it looks it’s better.

[oscarotero]

Great, thanks!