Idea: Decimal operators overhaul

[KarolS]

There are few incompatible changes to the BCD operators in I'm considering. As they are incompatible, they will have to go to the 0.4 version.

The BCD operators have two forms: +'/-' and $+/$-. I added the latter in 0.3.22 to make them more consistent (usually you use them with hexadecimal literals, so $) and more visually distinct, and to prevent parsing problems with character literals (currently, 'z'-'a' fails to parse). The idea was to eventually remove the old ones, but that obviously would be an incompatible change.

The *'/$* operator (BCD multiplication of bytes) seems pretty useless. Should it be removed in 0.4?

The same thing about <<'/$<</>>'/$>> (BCD mutliplication/division by 2):