code: func NewPremailer(doc *goquery.Document, options *Options) Premailer {
  	pr := premailer{}
  	pr.doc = doc
  	pr.rules = make([]*styleRule, 0)
  	pr.allRules = make([][]*css.CSSRule, 0)
  	pr.leftover = make([]*css.CSSRule, 0)
  	pr.elements = make(map[string]*elementRules)
  	pr.elIdAttr = "pr-el-id"
  	if options == nil {
  		options = NewOptions()
  	}
  	pr.options = options
  	return &pr
  }
docs: // NewPremailer return a new instance of Premailer
  // It take a Document as argument and it shouldn't be nil