whirl 0.3.1

• Improved error handling when the log cannot be created.
• Added new option environment_secrets to control which secret environment variables not to include in the log.
• Improved progress bar of run() to show all currently running scripts.
• Removed verbosity_level argument to run() since it is now completely controlled by zephyr options (see help("whirl-options")).
• Fixed bug where a script would not execute if using options(warn = 2) (#151)
• The log now distinguishes between directly and indirectly used packages, and visually highlights their approval status if a list of approved packages is provided.
• Added check for approved Python packages with the approved_python_packages option similar to for R.
• Improved how to find used Python packages, so it now only lists the packages actually used in the script.