Remove `.py` from usage description of command-line tools

[elshize]

Problem

When printing usage for any of the scripts in bin folder (e.g., rspeek), it prints out the name of the script file (with .py extension), e.g.:

usage: peek.py [-h] [--output [OUTPUT]] [--delimiter DELIMITER]

Expected

It should print the actual name of the program:

usage: rspeek [-h] [--output [OUTPUT]] [--delimiter DELIMITER]