Use Field Names to Initialize Structs

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

Bad	Good
```go k := User{"John", "Doe", true} ```	```go k := User{ FirstName: "John", LastName: "Doe", Admin: true, } ```

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

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

Struct Field Key