Deduction guides for std::unique_ptr

deduction_guides.h — deduction guides with some helper metafunctions.

test.cpp — compile time tests.

Notes

• New customization point template<class> constexpr bool deleter_applicable_to_array introduced. By default it is equal to true for default_delete<T[]> and is equal to false for everything else. It is necessary for deducing first template argument of unique_ptr as T[]. Possible alternative is to require from deleters inner typedef applicable_to_array (similarly to is_transparent for comparators).
• Deleter type is never deduced as a reference except for function types.
• For the deduced type UP following invariant holds
  • type UP::deleter_type::pointer is ill formed or
  • is_same<UP::element_type, pointer_traits<UP::deleter_type::pointer>::element_type>.