forth: Make exercise schema-compliant

[rbasso]

Related to #625.

[petertseng]

Note that even though you have given every group its own property, I was under the impression that the student is only expected to implement a single function (call it evaluate) - I don't think we would ask the tests to call a parsingAndNumbers function , an addition function, etc., as asking the student to implement all these functions separately seems to restrict freedom. So for any test generator, the generated code is possibly independent of the property.

Given this, I do question the property (I think there only needs to be a single value for it, "evaluate"), but it is also possible it is intentional, so if it is then I have nothing more to say.

[rbasso]

You are completely right, @petertseng! Thanks for catching that! 👍

Any recommendation for the property name? run? forth? Ops...didn't saw you already had answered that. 😬

[petertseng]

My initial thought was evaluate, but your suggestions of run or forth seem reasonable as well. Since all seem reasonable, I suppose we can just pick one, since there will only be one for the exercise (unless we make changes! in which case we can rediscuss then)

[rbasso]

Rewritten with evaluate, @petertseng!