Fetch one contact by either "id" or "external_id".

One of the "id" or "external_id" parameters must be specified.

Example Result:

{
  id: 1,
  external_id: "yourid",
  name: "Fred Smith",
  first_name: "Fred",
  last_name: "Smith",
  zip: "97701",
  address_book_id: 123,
  address_book_name: "Apptoto Address Book",
  writable: true,
  notes: "Long string of notes",
  deleted: false,
  phone_numbers: [
    {
      id: 3,
      number: "650-555-1212",
      normalized: "+16505551212",
      type: "mobile",
      is_primary: true
    }
  ],
  email_addresses: [
    {
      id: 4,
      address: "fredsmith@gmail.com",
      type: "work"
    }
  ],
  custom_data: {
    field_1: "vip"
  }
}