Add warning messages, tracing and a debug mode to the rewriter

[Kieranoski702]

The rewriter is currently very hard to debug. Some features that have been suggested that would help with debugging are:

• A warning that detects if applying a rule is outputting the same expression that was used as an input. This would go into a debug mode as this will affect performance
• A warning which detects cycles i.e. keep a history of all the models on each step, if models repeat then there must be a cycle. This would go into a debug mode as this will affect performance
• A trace that prints out the model at every step (possibly to stderr?). This could have two modes, one where it just shows a sub-expression changing to a different sub-expression and another which shows the full models at each step. This should be separate from the debug mode as this should not affect performance as much but it should still be an optional argument