Use Field Names to initialize Structs

You should almost always specify field names when initializing structs. This isnow enforced by go vet.

k := User{"John", "Doe", true}

k := User{
    FirstName: "John",
    LastName: "Doe",
    Admin: true,
}

Exception: Field names may be omitted in test tables when there are 3 orfewer fields.

tests := []struct{
  op Operation
  want string
}{
  {Add, "add"},
  {Subtract, "subtract"},
}