Updated brew_installs.sh and make_symlinks.sh

~ I did some small changes to the brew_installs.sh script, changing the
  order of the commands around and changing the "does brew exist?"
  conditional.
+~ Major surgery to the make_symlinks.sh. Now looks better, should
   function better. I also added a backup functionality, still needs
   testing though, the whole thing.
Small change to make_symlinks.sh