Updated a few URLs + handbooks

[briatte]

I recently assembled a small list of good R handbooks. Many of them are free online, and are also available as printed books in parallel.

The PR contains only a few fixes and one addition (Irizarry, which is more up-to-date than the Peng books in the list).

Let me know if you want me to submit more. I can also remove older resources when relevant.