create (GemPlugin::Manager)

    # File lib/gem_plugin.rb, line 156
        def create(name, options = {})
          last_slash = name.rindex("/")
          category = name[0 ... last_slash]
          plugin = name[last_slash .. -1]

          map = @plugins[category]
          if not map
            raise "Plugin category #{category} does not exist"
          elsif not map.has_key? plugin
            raise "Plugin #{plugin} does not exist in category #{category}"
          else
            map[plugin].new(options)
          end
        end