Make sde compare output in the order that variables are evaluated

[chrispcampbell]

Currently if you don't provide a spec.json file and then run sde compare, it will use the order that the variables are defined in the Vensim dat file. For diagnosing differences between Vensim and SDE, it's usually most helpful to see differences in the order that they are evaluated by SDE:

• const vars
• lookup vars
• data vars
• init vars
• aux vars
• level vars

That way, if there is a small difference in one of the earlier steps that causes cascading effects, it will be clear from the output of sde compare.