Misc. changes, file renames

Renamed get-headings.rb and make-table.rb to use underscores instead
of dashes.

db_helper.rb --
removes dependency on the not-included dbi_patch.rb;
this patch speeds run time by a trivial amount compared to total run-time.

dump_from_db.rb -- implements command-line arguments to pick output dir &
which submissions to dump (instead of having to change the code.)

get_headings.rb -- better wording in Usage string