Add read from stdin and write to stdout for key data input and output

I suggest that the losscalculator replaces the -e option with an input filepath and the -r option with an output filepath. This way, the calling syntax would be:

python3 damage_calculator.py [OPTIONS] REQUIRED-OPTIONS exposure-filepath result-filepath

Additionally input from stdin and output to stdout should be implemented for the main input and output so that these can be piped.

\rfc @cnievas, @shinde \approve @fd, @ds