DB48X: HP48-like RPL implementation for DM42

[c3d]

DB48X v0.4.9 is out, and has full support for HP48-style units, but modernized:

• Has recent SI prefixes, Z (zetta), Y (yotta), R (ronna) and Q (quetta) for large scale, z (zepto), y (yocto), r (ronto) and q (quecto) for small scale.
• Take into account the impact on unit conversions of the revised 2023 definition of the US Survey foot.
• Use exact (fraction-based) conversions wherever possible. This notably matters for the conversions of pre-2023 US Survey units, where the ratio is 1_ft = 1200/3937_m, which is not well represented using decimal values.
• Add computer-related units, like the byte, the bit, the baud, as well as a menu supporting these units.
• In order to support the computer-related units better, also recognize the power-of-two variants, e.g. 1_kiB is 1024_B. Also recogize the K prefix in addition to k.
  

YouTube quick demo: https://youtu.be/_KXT2-JXN-w
https://youtu.be/_KXT2-JXN-w