New package: `puppet-mode'

Not proud of it but still can't avoid Puppet.
Delete 'post-install.els'

After moving to `use-package' based package installation verification,
bootstrapping doesn't require user execution of any Emacs Lisp code.

I forgot to delete this file in commit 7637996e.
Pull in updates to Tomorrow theme

From https://github.com/chriskempson/tomorrow-theme
We can live without `customize' feature

Simplify things for today.  `custom-file'  (which we forgot to globally
define) housed mainly the current theme and noise from theme white
listing.  Let's get rid of it altogether and try living without the
`customize' system.