Enable multiple gists

[amorriscode]

I'd like to handle the following:

• A single gist that shows one book from read and currently-reading (this is the current implementation)
• A single gist to show the last 3 books from read and their rating (out of 5)
• A single gist to show ~3 books from currently-reading

We could handle this by just allowing the user to input 3 gist IDs and update them accordingly.