Let ck::Array<> derive from std::array<>

[poyenc]

The ck::Array<> and std::array<> behave same. And the only difference between those two types is that former has templated assignment operator. I think ck::Array<> can be used in most use case which std::array<> is needed, so ck::Array<> should inherit std::array<> in order to be compatible with most of interfaces.

Before

template <typename TData, index_t NSize>
struct Array

After

template <typename TData, index_t NSize>
struct Array : std::array<TData, NSize>