Add aliases for newly discovered --word-diff

dotfiles/gittum/main.gitconfig

   slurp = ! ~/.gittum/bin/slurp
   st = status
   sh = show
+  sw = show --word-diff=color
+  swp = show --word-diff=porcelain
   who = ! ~/.gittum/bin/who
   whoo = ! ~/.gittum/bin/whoo
   xtragc = ! ~/.gittum/bin/xtragc