GitHub link + small fix

I've updated the page with a link to the files on GitHub, if you prefer to download them through that, and also updated the files slightly with one bug fix + a few minor additions.

The fix: when initializing an achievement without an explicitly provided ID, it was supposed to generate an ID from the name, but incorrectly did so from the ID (which didn't exist). You won't run into this problem if you're already declaring IDs for your achievements (and manually declaring IDs is the preferred solution for Steam integration).

The additions:

• Timestamps have better error checking so if something goes wrong, you shouldn't end up with an error screen.
• If the game detects it's in the initialization phase, it will not attempt to show the popup screen. This means you can grant achievements in an init python block if required to retroactively turn an old achievement system into this one (typically by checking for a persistent variable and then granting the achievement accordingly).
• There's a config value in achievements.rpy to turn off in-game popups altogether if you'd just like the in-game achievement gallery or the Steam integration

If you have a use case you want to use the achievement system for which isn't covered, let me know and I'll see if it'd be suitable to incorporate into the system itself! I hope you find it useful for adding achievements to your games ✨