Dropbox issues fixed

Just a quick note to let you know that since Dropbox have made some under the hood changes, some links on the website stopped working, most importantly the ones that let you download Scienceville when you sign up for my mailing list. It's fixed, so far as I can tell, and if it isn't, then be sure to let me know in the comments. And if for any reason you've tried to download the books and failed, again, let me know and I'll email a copy personally.