Update README

It could be a lot better, but it's not as bad as it was.  All of the
very outdated information has been removed and some better info has been
added in its place.

Return a 404 error when static files aren't found

Fix release script

The release script wasn't deleting the windows binary correctly before
building everything else, so it was getting packaged into everything.

Add MIT license

Also added a link to PhotoSwipe in README.md

Fix missing games.json error; Small fixes

- Don't freak out if games.json doesn't exist, just go get it.  And
don't bother looking for a specific appid in updateGamesJson().
- Fix games.json caching issue (nil pointer).
- Tweak exists() to return only a bool
- Bail if main() can't load settings.

Fix CSS on thumbnail page

This required a small change to the main page's structure.  A div after
the #container was added to match the thumbnail page's #thumblist div.

Add a batch file to build releases

So far the only releases built are windows/386, linux/386, linux/amd64,
and linux/arm.