[boost] introduce boost::utility::ios.hpp

For easy handling of various stream operations I would like to provide a small library: * queries stream properties * supports defaultfloat/hexfloat * provides conversions for stream::floatfield <-> FP std::chars_format in C++17 + getter/setter + std::setfloat * provides conversions for numeric output of u/int8_t * small stuff like std::tab Summa summarum This makes it much more pleasant to work with than manually fiddling around with stream::flags. thx Gero