DB48X: HP48-like RPL implementation for DM42

[Dashier]

There's a Facebook thread regarding a test of calculator accuracy based on an exam question that results in:

Code:

 (SQRT(2)-1)^10 = 3363-2378*SQRT(2)

There are a number of comments regarding the accuracy of various calculators.

I elected to set the DB50X to 2000 digits precision and test it. The difference between the LHS and RHS was 2.15651x10^-1997

Nice job Christophe!