[C++] char16_t / char32_t

http://en.cppreference.com/w/cpp/language/types

char16_t and char32_t are guaranteed unsigned.

N4296 3.9.1 [basic.fundamental]/5: "Types char16_t and char32_t denote distinct types with the same size, signedness, and alignment as uint_least16_t and uint_least32_t, respectively, in <cstdint>, called the underlying types.