DB48X: HP48-like RPL implementation for DM42

[mahi]

Thank you for the interactive stack, Christophe! I really like it!

Concerning overwriting the *.csv files... Maybe add support for custom *.csv files? For example "units-custom.csv". The custom entries are appended to those of the regular csv. In case of duplicates, the custom files gets preference. This way you can safely overwrite the regular csv files without risk of losing the custom entries.

Just an idea. It might need to be thought out better before implementing.