Sort by data-attribute

[fisherspoon]

Hi, your library can sort by dates, but my date format is (02.19.2020)
Therefore, I would suggest adding the ability to sort by date attribute in which you can, for example, put time in milliseconds

[LeeWannacott]

Hey, I have seen some other libraries using data-attributes and I considered it early on; I try to have as much out of the box as possible, however, I should add this for any sorting edge case the library doesn't sort. I would want to make it as generalisable as possible, so the user can put anything they want after data (not just data-dates) assuming its consistent.

[LeeWannacott]

Added in commit: ee8e7b9 . Users can now use <th class="data-sort"> with <td data-sort=""> to sort by data-attribute rather than the values of the tables column clicked on. Thanks.