littlefs-do: Parse C++ class Settings to reduce maintenance burden

[NeroBurner]

happy you like the settings command, unfortunately it is high maintenance, but I like it as well :)

Theoretically, it should be possible to parse the class Settings to discover the fields of the settings at build or run time. Probably not easy to do, but that would reduce the maintenance for this feature :)

Originally posted by @JF002 in #52 (comment)