Documentation changes, class name changes, runAsService()

WARNING: These changes are incompatible with the current version and will break existing code!

These changes make rename some classses, to make them consistent with the documentation: Renamed LogsFieldExporter to BigqueryFieldsExporter and LogsFieldExporterSet to BigqueryFieldsExporterSet.

The readme file is expanded, to include some things that I needed to do to get things working.

The parameter run_as_a_service was always true, but I did not have sufficient permissions and introduced the possibility to make this false.
Lets just change the docs to make the names consistent instead of having users have to change their existing code