The function extracting the firmware image for .hex and .bin files
wasn't working correctly: it only extracted the .text segment and not
the .data segment.
This commit fixes this issue, so that it behaves (hopefully) just like
objcopy -O{ihex|binary}.
Another small change is that the formatting of the .hex file was made
more like the output of objcopy: no entry addres (old Intel CPU
holdover) and 16 bytes of data on each line.
