Enable LookAhead and/or Recursive Processing

[joffemd]

PSCF models are processed unidirectionally. Formulas can only reference prior year values or current year values that have already been processed (i.e. are higher up in the list of Series). It would be great if this restriction could somehow be relaxed so that expressions could be influenced by values that would normally be calculated later.

This requirement needs discussion before anyone attempts to implement it.