Though I don't understand why there's so much public API documentation in this file. A lot of this stuff should be in [our docs](https://github.com/gregbell/active_admin/blob/fe5becdb49ab74bf209bedc7bce456aa345070be/docs/3-index-pages/index-as-table.md).

Wait... the text in that file is __very__ similar to the comments here...

@vjt would you mind pushing your added documentation to that file, and remove any duplicated docs that are in this file? Duplication is bad.