def manifest
    if File.exists?(manifest_file) && File.readable?(manifest_file) then
      MultiJson.load(File.read(manifest_file))
    else
      {}
    end
  end
def manifest
    if File.exists?(manifest_file) && File.readable?(manifest_file) then
      MultiJson.load(File.read(manifest_file))
    else
      {}
    end
  end
Retrieve the command's Manifest, loading it from disk if necessary
 If no Manifest is available, returns an empty hash

 @return [Hash]