Update dotfiles script to automate xCode CLI tools

- Create a script to check if xCode is installed; if so inform the user,
  if not run automated install script of xCode CLI tools
- Create a recursive script to automate xCode CLI tools; checks version
  of kernel to ensure user is on 13 or up (Mavericks) as thats when
  `xcode-select --install` was introduced.

Issue: #33