Two-colour PERPL, install with pip

Installation is now with pip, including from PyPI: pip install perpl
Includes installation of terminal commands to run scripts

Two colour PERPL, updated to Python 3.11

Functionality for two-channel relative positions, within and between channels.
Update to set up and run in Python 3.11 environment, fixing a recent Jupyter notebook compatibility issue.

Two-colour PERPL

Adds functionality for two-channel relative positions, within and between channels.