Adds Github Actions autobuild and build check

[jopbastard]

This adds some extra Github Actions setup to automatically commit to the gh-pages branch any time master receives a commit. It will also check any other branch that receives commits to see if the build is successful. (Also checks pull requests.)

To enable, you need to make two repository settings changes. Go to the Actions section and turn on "Read and write permissions" for workflows:

You also need to adjust the Pages settings to pull directly from a branch instead of using the built-in Jekyll action:

[Pinkfag]

mixed feelings about getting help from one of the thread shitposters...

[jopbastard]

I did consider editing the background image, but decided against it. :P Take it or leave it; no hard feelings either way.