bin.example-nanoc: rewrite to support Rubies, rolo

The script now supports system Ruby or Rvm (1.9 or 2.0). The rolo
gem is also used to prevent nanoc/guard from running twice

We also remove :nohup support, because user can help...
bin: remove the :core scripts
README: + new notes about the diff. between 2 branches

The two branches :core and :master are now very different. I do not
now why this happens. But this is very true. We now do not want to
develop :core features on :master, nor to develop :users stuff on
the :core -- that should be used for Ruby scripts
etc.web: delete :core config. from the :master

The web configuration is now on :core branch