Custom sort order for model annotation

[lucker14-zz]

We would love to implement custom sort to this gem. It should let you decide the order of output, because sometimes you don't want the order given in classified sort.

How I would do that:
Add new option parameters 'sort_order' - array representing the order of output e.g. ['pk', 'associations', 'rest_cols', 'timestamps'] and boolean param 'custom_sort'.
The sort method could be almost entirely same as classified_sort, only difference being the last line where instead of

([id] << rest_cols << timestamps << associations).flatten.compact
would be something like

(sort_order[0] << sort_order[1] << sort_order[2] << sort_order[3]).flatten.compact

I am able to make this PR if you're interested.

[ctran]

All pull requests are welcome when they satisfy the following:

• Not break existing behavior
• Useful for others (general enough)
• Pass CI

Regarding this, can you tell me more about its motivation? Why is a custom sort order useful?