Preprocessor update

— Rework the function that handles the macro-expansion of the .mod file
— Rework equation tags (preprocessor#38)
— Provide M_ as an output to stoch_simul and discretionary_policy (!1711)

preprocessor @ 9ff10f48

-Subproject commit abedb47573317dd16089b72cb95d0abca3893f6a
+Subproject commit 9ff10f482aa51c23c7fe4fd5be4b66295c871179