code: func NewV3MailInit(from *Email, subject string, to *Email, content ...*Content) *SGMailV3 {
  	m := new(SGMailV3)
  	m.SetFrom(from)
  	m.Subject = subject
  	p := NewPersonalization()
  	p.AddTos(to)
  	m.AddPersonalizations(p)
  	m.AddContent(content...)
  	return m
  }
docs: // NewV3MailInit ...