allow specification of array memeber

Permit array member via passing a `CFunc::CArray` or a Array of [type,size]

```ruby
class  STest4 < FFI::Struct
  layout :x,[:int8,10],
	  :y,:int16,
	  :z,:int32
end

def assert m="" ,&b
  res = b.call
  if !res
    s = :failed
  else
    s = :ok
  end
  
  puts "#{m}: #{s}"
  
  return res
end

assert "Size is 16" do
  p STest4.size
  16 == STest4.size
end

assert "0 less than aligned" do
  0 < STest4.align
end

stest = STest4.new

10.times do |i|
  stest[:x][i] = 10 + i
end

stest[:y] = 20
stest[:z] = 0

10.times do |i|
  assert do
    10 + i == stest[:x][i].value
  end
end

assert do 
  20 == stest[:y]
end

assert do 
  0 == stest[:z]
end

```