Fixes #2  Config is now read out of a YAML file.

The config file is now loaded from dotfile.conf which is a YAML file.  Format is
---
rules:
  -
    action: symlink
    file: __HOME__/.dotfiles/prezto
    target: __HOME__/.zprezto
  -
   action: symlink
   file: __HOME__/.zprezto/runcoms/zshrc
   target: __HOME__/.zshrc
  -

etc