Converted documentation to AsciiDoc (Christian Mazakas).

Added noexcept and constexpr as appropriate.

Marked obsolete functions as deprecated.

Removed obsolete compiler workarounds.

Changed array<T, 0>::begin(), cbegin(), end(), cend() to return nullptr, enabling constexpr. This matches the behavior of std::array.

Removed local hash_value overload; boost::hash supports array-like types natively.

array<T, 0> can now be initialized with = {{}}.

Added operator<=>.

Added to_array.