A synthetic example of decision-focused learning

[jonpea]

Overview

New/Updated file	Notes
examples/decision_focused_learning/predict_and_optimize.ipynb	A example of Neuromancer applied to a 2D predict-and-optimize problem
examples/decision_focused_learning/predict_and_optimize.py	Generated from the notebook with jupytext
examples/decision_focused_learning/datasources.py	A utility module for splitting datasets into train/dev/test partitions - perhaps also useful in other examples
pyproject.toml	Added new dependencies for the example
INSTALLATION.md	I regenerated the table of contents and added brief instructions on creating a virtual environment with venv (rather than conda)

Many thanks!