Suggestion : sort by role

[migueldhyne]

First of all, thank you for this useful plugin !
I use it in order to collect comments from teachers to students.

My first suggestion is : give the possibility to sort users by role

My second suggestion is : during the export in excel format, allow one line by comment (if a student receives 10 comments, 10 lines are created in the excel file). I will be easier to read and print.

Thank you !