[Feature Request] Keep old results and read path list from file (for incremental scans)

[RaymondBakerIBM]

To facilitate incremental scans, we need to keep old results in the baseline instead of the default behavior of deleting all files which weren't scanned in the current scan.

Sometimes there will be too many paths to pass into the cli (larger than ARG_MAX) so there needs to be another way to provide paths. stdin is already used for the baseline file so pass it in as a path for the program to read.

Associated PR
#153