Progamming and use of user flash page for data.

This example project uses the EFM32 CMSIS  and demonstrates the programming of
the user page in flash. The page can be used for data such as keys, serial
numbers and other information that should not be deleted by a device erase.

PB0 increases the main counter
PB1 saves the main counter value to the userpage, and displays how many writes
have been issued.

Board:  Silicon Labs EFM32WG_STK3800 Development Kit
Device: EFM32WG990F256
