Fix forgotten version update
Use stdbool.h
Rework NV storage

Separates IEC/IEEE-488 settings which fixes #19.
Stores common settings (not bus dependent) as well.
Platform specific code reduced to functions for reading/writing bytes.
NV settings stable across different compiler/versions as the NV storage
locations are no longer generated by the compiler but by the code itself.
Unfortunately, this instability prevents an automatic conversion from
NV data stored in the old format into this new one.
Merge branch 'master' of https://github.com/fachat/XD2031