Add --reload-dir argument

[montaguegabe]

This is a small change that partially addresses #318, and allows multiple reload dirs to be specified via the CLI instead of using just the CWD, using the --reload-dir option, which can be passed multiple times for multiple reload directories.

Why I need this:
I use TaskIQ with tasks loaded from pip packages that I've installed with pip install -e path/to/local/package in development, and am constantly editing and having to manually reload TaskIQ due to the fact that the locally-installed package is outside of the CWD.

• If the --reload-dir option is not passed, the default of using the CWD is still used.
• pytest tests still pass
• Committed with pre-commit hooks installed and working
• Adds a logger.debug of the reload dirs being watched.