Implement the `redi_lib.transfer_pfe_tree()`
which sends to REDCap all events of one form in one request
Timing: ~15 seconds without skipping blanks
122:+    # TODO: Add code to allow keeping track of `unsent` forms
125:+    # TODO: Replace `skip_blanks` boolean by a parameter sent in the command line
188:+    # TODO: add column in the report: study_id -> total_events parsed