Implement rounding and improved comparison

[ckormanyos]

Implement rounding and improved comparison using individual base-10 digit(s) slightly beyond the digit of least significance instead of entire limbs and even if these least significant digits are within the middle of a given limb or separated between two limbs.

Incubate this technology here in wide-decimal. When this technology is stable, port it over to cpp_dec_float in Boost.

[ckormanyos]

Round on floor/ceil/integer-cast has been successfully implemented in 6544d13.

This would theoretically be enough to handle the mentioned boost issue in cpp-dec_float (which is unrelated to this project, but similar).

Let's establish some experience with this rounding here and maybe i can see how it shakes out in a boost PR shortly.