"Getter" for `payoff_arrays`

[oyamad]

What is the proper Julia counterpart of QuantEcon/QuantEcon.py#382?

1. Add a field payoff_arrays to NormalFormGame:

   struct NormalFormGame{N,T<:Real}
       players::NTuple{N,Player{N,T}}
       nums_actions::NTuple{N,Int}
       payoff_arrays::NTuple{N,Array{T,N}}
   end

   This seems not to be very Julian?
   And this requires adding the same code of generating the tuple to many constructors.

2. Add a method payoff_arrays to NormalFormGame:

   payoff_arrays(g::NormalFormGame{N,T}) where {N,T} =
       tuple([player.payoff_array for player in g.players]...)::NTuple{N,Array{T,N}}

   This is what I had in mind initially, but now I want to avoid this as it will introduce a conflict with the likely usage of payoff_arrays as a variable name.

3. Name the above method get_payoff_arrays:

   Sounds too long? And to "get" payoff arrays, one could just call g.players[i].payoff_array.