Configuration menu reorganization

Eventually, I'd like to add support for multiple date and time
formats, as well as a temperature display in Celsius or Fahrenheit,
But these options do not fit under any of the "cfg" submenus. So the
"cfg time" submenu is now labeled "cfg regn" (configure region).
Some day, "cfg regn" will contain additional options for date format,
time format, and temperature units ("date fmt", "time fmt", and
"set °C.°F").

This release also includes new configuration options in config.h:
GPS timekeeping, automatic dimmer, display voltage range, and USART
baud rate.  Most notably, firmware support for hardware hacks may now
be enabled and disabled at compile time.