Provide a C++17 stdx type traits implementation

C++14 offers nearly all of the compiler support required to support the full universe of C++17 type traits.

In particular:

• variable templates for values
  • is_pod<T>::value -> is_pod_v<T>
• C++17 traits
  • void_t, is_(no)throw_swappable(_with), (con|dis)junction, negation, bool_constant, etc.

These make template meta programs dramatically easier to read by reducing line noise.