stm32_i2c: handle more error conditions on I2C bus

this fixes a I2C ISR storm condition where status=0x70084, which can
happen with some specific types of noise on the I2C bus. This was
reproduced by playing 80s rock through a Jabra wireless headset close
to the I2C cables.
Merge pull request #23 from tridge/pullrequest-i2c-lockup-fix

stm32_i2c: handle more error conditions on I2C bus
Force a hardfault on stack overflows to make the fault condition obvious once it occurs
Cleanup of docs / comments
lib_sscanf: fixed a hang in scanf() on end of string

if we reach end of buffer when we are not on a format specifier then
the code would loop forever.
Merge pull request #24 from tridge/pullrequest-sscanf-hang

lib_sscanf: fixed a hang in scanf() on end of string
ARM math.h: Remove commented out code parts
Fixing md5 hashing when digest[$i] lower that 16.  Sergey <sectus@mail.ru>
Added WIP F102 support for the MAvstation
updating pinmap for mavstation