the function:
virtual size_t AP_HAL::Print::write(const uint8_t *buffer, size_t size);
was hidden in all derived classes by their
virtual size_t write(uint8_t) = 0; implementations.
To solve this, a non-virtual write(const uint8_t *, size_t) that calls a
virtual write_implementation was added.
This isn't necessary atm, because the derived classes don't call
write(const uint8_t *, size_t), BUT this decreases the apm2-quad Program
size by 40 bytes :D and removes warnings.
* BetterStream Means AP_HAL depends on AP_Common, for now, in order to have
the AVR specific pgm_char_t defined.
I'll need to factor that out in the future but for now it can stay