Allow for equations to be entered as answers in answerableComponents

[mstachowsky]

At the moment, if I have

`!assignmentVariables

!var %x:1:10:0
!var %y:10:100:0
!var %z: %x + %y

!endAssignmentVariables`

and I want an answerBox whose answer is %x + %y, I have to set the answer as so:

!ans numeric:%z:absolute id1

This means I have to create a new variable each time I want an answer, even if it is a relatively simple equation. I should be able to write this:

!ans numeric:%x + %y:absolute id1

However, this is not possible.