use latest inputs
add fileExists
remove the hardcoded filenames

Details:
- remove the hardcoded input/output file names.
- add the set* functions
- check and bail out when the inputs dont exist
- check and warn if the output exists
- Verified that the output is the same as before
do not iterate on invalid inputs
print file contents only when dbg
delete-trailing-space
allow to specify input/output on cmd-line

Details:
by default leave the files I'm currently using