Close access to local files

This example is excellent, but the way it is implemented might lead
people to think this is how it should be done in production.  However,
since no local files are actually needed here, it is better to show
a pattern that doesn't open up access to local files.
Merge pull request #128 from xogeny/use_data

Close access to local files
Merge branch 'master' into prefixsubscribe