Easy. First, it's a spin off of the phrase "Code Monkey". Take a gander over at the entry in the jargon file:
A self-deprecating way of denying responsibility for a management decision, or of complaining about having to live with such decisions. As in “Don't ask me why we need to write a compiler in COBOL, I'm just a code monkey.”
There's even a show called Code Monkey which stunning animation brings back memories of playing far too many video games in the 80's.
I'm abusing the word codex a little here. It tends to be used mostly for manuscripts and frequently religious ones as well. However, as a word it has the handy property of dealing with books and being very close to code. But truth be told this blog title would be more suited to a programmer who worked in a rare book and manuscript library. If someone fits the bill and complains, I'll let them have it if they can think of a better name for me ;).
I've also seem to recall having seen codex be used in the sense corpus is used in analysing text and writing. Of course, this could just be my faulty memory. I thought about using corpus monkey, but that's a little too close to corpse monkey, don't you think?