New Rounding Control

I decided to just go ahead and let people control rounding just as they can control precision. So, I added two functions to the base standard library to handle that. I also modified the other standard library to be robust to any rounding mode in use, and then forced most functions to just use a specific rounding mode every time. And that rounding mode is a new mode that was added: the double rounding mode of 05 AWAY.

Included libraries (from Cygwin for mingw64-x86_64; I still don't see a need for the latest changes to upstream ncurses, they are just fixing compiler warnings and documentation):
GMP : 6.3.0-1
libstdc++ : 11.4.0-1
ncurses : 6.4-20230812