Removing the entire `source/tutorials` directory

as these files are sourced from the `tutorials` submodule repo. These
files should *never* be edited locally, and that wasn't clear unless you
read the documentation, so hopefully this will prevent it from happening
again.
Updating to latest `tutorials`

which applied this commit to the right repository:

    commit eb4e5c850702fe26b0e57729c68f28abfd36bdb4
    Author: Mike Naberezny <mike@naberezny.com>
    Date:   Sat Sep 27 13:53:24 2014 -0700

        Fix Nokogiri::XML::ParseOptions example