C++20 <version> and expanded <type_traits>

[ZERICO2005]

C++20 <version> provides macros to indicate which parts of libcxx are supported. For now, I have only defined the ones that should be fully supported

// c++14
__cpp_lib_exchange_function
__cpp_lib_integral_constant_callable
__cpp_lib_is_null_pointer
// c++17
__cpp_lib_as_const
__cpp_lib_bool_constant
__cpp_lib_logical_traits
__cpp_lib_void_t
// c++20
__cpp_lib_bit_cast
__cpp_lib_endian
__cpp_lib_math_constants

A few others are mostly complete such as __cpp_lib_transformation_trait_aliases and __cpp_lib_is_swappable

[ZERICO2005]

I have fixed this issue #534 by #ifdef'ing the three functions out. This allows the <type_traits> and <utility> header to compile without errors in C++11. However, std::swap and std::move are C++11 functions, so those may need a specific C++11 implementation.