gitversion: Include git revision in sourcecode

There is now a file, "gitversion.h", that exports a variable that reflects
a build's git version.
support scripts: Use "sudo" for non-root access

Development is no longer being done as the root user.  Therefore, wrap
the GPIO calls around sudo, to allow non-root users to run the scripts.
gg: Add call to query number of cells

The number of cells is stored in flash, and is not available through any
other means.  Add a call to read this value out of flash.
Makefile: Rename "pmb" to "senoko" in output files

This will cause us to generate senoko.bin instead of pmb.bin.
chg: Kill host/charging when voltage goes too low/high

When the battery voltage goes out of range, kill the host system,
or stop charging.  This will prevent the battery from failing catastrophically.