Remove plugin-specific files from gemified library
Update meta files
Add .gemspec and gemify ./lib/ directory
Require the supporting Nessus libs
Add Engine and Version files
Improve Nessus base classes with enhancements from Dradis Pro
Make the Nessus plugin use the ContentService and TemplateService defined in Dradis::Plugins
Importer - make use of the new :all_issues_by_field method in ContentService