Unify interface with SDDP.jl

[odow]

trafficstars

Ref https://github.com/odow/SDDP.jl

[odow]

• Get rid of constraints and terminal cost.

m = SPModel(stages=3, sense=:Min) do sp, t
    @states(sp, begin
    end)
    @controls(sp, begin
    end)
    @noises(sp, begin
    end)
    dynamics!(sp) do out_state, in_state, control, noise
        if control[u] == 1
            return DynamicProgramming.INFEASIBLE
        end
        out_state[x] = in_state[x]+1
        return noise[w]
    end
end