Support calculated values from multiple formula engines

In OpenFormula, it's possible to do formula including a way to
describe non-standard formula.

It would be interesting to be able to add information about formula
engines and values.

What would be interesting is to be able to do is the following:
Letting the formula's be calculated with a formula engine.
Saving the cells values with a calculated value attribute and formula
engine attribute.
Calculate the formulas with another formula engine.
Saving also the new values with a calculated value attribute and
formula engine attribute.

It needs something to preserve the calculated value of that cell and
which formula engine that did it. Preferably in a way so that multiple
values from multiple formula engines and versions can be stored
parallel.

To avoid problems, software should, without extra input, show the most
recent results.

A function to show the name of the formula engine currently used would
be handy.
Also a function to show a list of all formula engines (+version if
applicable) with their values.

This would be very handy to compare things from different formula
engines in the future.

Was inspired by the bottom of this blog post, where formula engines
are mentioned:
http://www.robweir.com/blog/2010/07/odf12-public-review.html