def add_plugin(dir, entry_script = nil)
      append_runtimepath(dir)
      if entry_script
        entry_script_path = Path.new(entry_script)
        command("runtime #{entry_script_path}")
      end
    end
def add_plugin(dir, entry_script = nil)
      append_runtimepath(dir)
      if entry_script
        entry_script_path = Path.new(entry_script)
        command("runtime #{entry_script_path}")
      end
    end
Public: Adds a plugin to Vim's runtime. Initially, Vim is started
 without sourcing any plugins to ensure a clean state. This method can be
 used to populate the instance's environment.

 dir          - The base directory of the plugin, the one that contains
                its autoload, plugin, ftplugin, etc. directories.
 entry_script - The Vim script that's runtime'd to initialize the plugin
                (optional).

 Examples

   vim.add_plugin 'rails', 'plugin/rails.vim'

 Returns nothing.