- store name+callback pairs in list instead of a hash map
remove vector reserve() overhead
- rework callbacks to expect flash strings
- comments...
Small difference is that now there's no way to know if command already
exists. Meaning, while we do override the existing callback, comman
names list will have more than one entry.
Flash strings are quite weird. In case we finally get all `const char*`s
in PROGMEM (which is the case for ESP32?), this could use a comment-proposed
method of having handlers per-module instead of handlers per-command.