Add `--outfile-keep` flag to keep outfile on termdown exit instead of deleting.

[ediw8311xht]

Purpose:

Issues such as: #54 , show confusion on how outfile works, and expect that the outfile will not be deleted on exit.

Changes:

Added --outfile-keep flag to keep outfile on termdown exit instead of deleting. This flag defaults to False.

What this Accomplishes:

This change adds an option that allows for the outfile to be kept. Also ensures that users know that the default behavior of --outfile (automatically deleting the outfile on exit) is not a bug.