Duh, Clojure's PersistentVector is maintained at github

I've been coding against an older version of the code. Duh. The latest PersistentVector code can be found at github.

https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/PersistentVector.java

So I've updated my F# version at github to be a relatively literal translation of the clojure code. I'll probably tweak it a bit to take advantage of F# features and perhaps find better names that help me understand what is going on a bit better.