fix tuple_element: support SFINAE-friendly
add iterator_traits: SFINAE-friendly version
fix isolated files
fix net/endian.hpp
fix.
add variadic assert macro
fix.
add SPROUT_STATIC_ASSERT variadic macro version
support variadic macros for clang
fix cstdint.hpp
fix.
add algorithm for_each, gather
add SPROUT_AUTO_FORWARD