Dead/incorrect links

[esmale]

• The link to the "Code the Classics" book in the "Game Dev Resources" section redirects to https://filmstories.co.uk/news/, which has no content related to this book. I can find a variety of links to purchase the book via google, but the current link on this page appears to be dead.

• In the Animation chapter, there's a link for this text: "The DragonRuby GTK docs have a detailed example of how to do this.". That link is incorrect and lands you on a "404 - not found" page within the DragonRuby docs. I think that page that should actually be linked to should be: https://docs.dragonruby.org/#/samples/rendering-sprites?id=animation-using-sprite-sheet-mainrb

[brettchalupa]

@esmale thanks for reporting these issues, will work on fixing them!