introduce boost::utility::ios.hpp

From: Gero Peterhoff (g.peterhoff_at_[hidden])
Date: 2023-03-23 19:06:32

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