Strange MCUSR behavior workaround

When the microcontroller starts, this firmware checks the MCUSR
register to determine the reason for the reset and presents a suitable
diagnostic message on the display.

For whatever reason, the BORF flag is sometimes set in addition to
other reset flags when no brown out condition has occurred.  The brown
out detection reset message ("bod rset") is now displayed only if no
other reset flags are set.
Aging display compensation with autodimmer bugfix

The boost configuration settings can be increased in config.h to
compensate for an aging VFD display with fading phosphors.  Doing so,
however, could cause automatic dimming to behave erratically.  This
bug has been fixed.
Improved automatic display inactivation when dark

The threshold for automatic display inactivation when dark now has a
range of 1-8 on a logarithmic scale.  This behavior is more intuitive
than the previous range of 1-50 on a linear scale.  The new settings
also allow the darkness threshold to cover a larger dynamic range.