Parazoa - Immutable, persistent data structures for Nim

[sekao]

Yep I saw [your project](https://github.com/PMunch/nim-persistent-vector) and I 
worked off of the same [blog posts by 
hypirion](https://hypirion.com/musings/understanding-persistent-vector-pt-1). I 
still haven't implemented the tail optimization he wrote about in part 3 though 
but maybe I'll find the time during this break.