Run factorio in headless server mode

[terite]

For CI systems like travis it's difficult to get the full client for a couple reasons

• One needs to be logged in to download the full factorio
• Downloading 800 megabytes repeatedly from Wube servers would be slow (and lots of traffic)
• re-hosting the full version of factorio on an easier to access host seems like trouble

It would be nice if there was a way to run tests against the headless server. I got this working locally by doing the following

• call factorio.run() on the first tick
• intentionally error(...) after all specs have run to stop (crash) the server
• use --start-server instead of --load-game
• use a modified server-settings.json that does things like disabling matchmaking and auto-pause

The only major issue with this approach is that it's not possible to get a player in game. This means no GUI testing, or testing of anything that relies on a player.

The benefits are pretty nice however

• completely automated testing is possible
• quicker game loading
• easier to set up on CI.