Add cross-references after adding hyperref per #36

[jamesray1]

#36

Please put a hypertarget and hyperlink for some symbols. For instance, when I read the epsilon symbol for 2.11, I had to scroll back up (to 2.5) to remind myself what that was. With hyperrefs I could click the ref, read the target, and scroll back to where I was or use CTRL+F. Similarly, hypertargets and hyperlinks for “dependency”, “later”, “latest messages”, and “validator weights” on p. 7, 3.1, would be helpful for a refresher, particularly the latest message. Also for the helper function. Alternatively or additionally as @MicahZoltu suggested just have more meaningful variable names. Looking at other literature, the convention is to use single character variables. So just use hypertargets and hyperrefs, if anything, unless you want to break with convention.