DB48X: HP48-like RPL implementation for DM42

[c3d]

Pre-release v0.8.8 is available for testing.

The focus of this release is power usage reduction while on battery, to try to get closer to the original DM42 firmware. This goes through a severe reduction of animations while on battery, caching of object rendering on the stack, and using hardware-assisted DMCP routines to transfer data to the display.

The custom menu in this release has entries to store statistics about battery levels in a file called BAT.CSV on the disk. I would appreciate if various users who regularly use the machine on battery could record the battery level on a regular basis, so that we can build some reasonable evaluation of battery usage.