DB48X: HP48-like RPL implementation for DM42

[c3d]

The weekly release is out.

Nothing major (v0.7.17 was late), restarting work on symbolic operations, this time with SUBST, APPLY and WHERE (the | operator).

That | operator has a slightly different syntax for multiple substitutions, i.e. where the HP48 would have 'A+B*C|(A=X;B=Y)', DB48X currently only supports 'A+B*C|A=X|B=Y'. I find it easier to type and read. Does anyone really want the HP syntax, or is that used infrequently enough that manually adjusting is justified?