Huge refactoring for C++ and low-power mode

The display currently shows the time, with hours and minutes, and is
capable of receiving input with buttons (though does nothing). It
sleeps during intervals where nothing is happening. The display task
runs once per second, and RTC alarm A is used for periodic alarms to
update the system time.

.gdbinit

@@ -1,6 +1,5 @@
-tar rem :4242
 file watch.elf
-load watch.elf
+tar rem :4242
 
 set $PERIPH_BASE = (uint32_t)0x40000000U
 set $APBPERIPH_BASE = $PERIPH_BASE
@@ -11,6 +10,8 @@ set $RCC = (RCC_TypeDef *)(0x40000000 + 0x00020000U + 0x1000U)
 set $RTC = (RTC_TypeDef *)(0x40000000 + 0x00002800U)
 set $PWR = (PWR_TypeDef *)(0x40000000 + 0x00007000U)
 set $EXTI = (EXTI_TypeDef *) ($APBPERIPH_BASE + 0x00010400U)
+set $GPIOA = (GPIO_TypeDef *)($IOPPERIPH_BASE + 0x00000000U)
+set $LPTIM1 = (LPTIM_TypeDef *)($APBPERIPH_BASE + 0x00007C00U)
 
 set history filename .gdb_history
 set history save on