Auto constructor for structs

As a Engineer I want to automate simple constructors so that allocation of new type is an "arrow function: (A, B, C) => T" eliminates the boilerplate 

```go
type T struct {
  a A
  b B
  c C
}

var NewT = hseq.Arrow3[T, A, B, C]
```

As hypothesis we eliminate boilerplate:

```go
func NewT(a A, b B, c C) *T {
  return &T{a:a, b:b, c:c)
}
```