Faster access for tuple of arrays

[mcabbott]

This is currently much slower than LazyArrays.Hcat, surely it can be fixed:

LazyStack.jl/test/speed.jl

Lines 24 to 29 in 19889ac

	@btime hcat($t1...); # 178.379 ns (4 allocations: 1.03 KiB)
	@btime collect(stack($t1)); # 1.032 μs (2 allocations: 912 bytes) -- was quicker I swear
	@btime collect($(stack(t1))); # 1.065 μs (1 allocation: 896 bytes)
	@btime collect(Hcat($t1...)); # 149.001 ns (3 allocations: 1008 bytes) -- match this