Implemented division, modulo and example files

Natural division and modulo now work correctly, by implementing division naive algorithm and modulo basic calculation.
Plus created the Examples directory to save demo files.
WIP — Documenting

I’m documenting sources for further Doxygen use. More to come.
WIP #2 — Documenting

More docs for Doxygen. Plus implemented Digit::operator/=() and Digit::operator%=().
Started implementation of Integer and Rational