don't store local files within dotfiles
update setup method to avoid symlinks

* This removes setup.bat, which means setup on Windows requires Cygwin.
  Eventually I will (hopefully) add a Windows setup method, but for now, there
  is not one.
* ./setup.sh will also handle zsh config files. I may change this in the future,
  since this means machines without zsh will also get zsh configs, but for now,
  I'd rather just have one file to handle everything.
update readme