No documentation of what's in the task report's stats

[pierrecamilleri]

Overview

Statistics present in a task report are to my knowledge undocumented (# TODO: add docs).

However, there are non-trivial stats in there : for instance, report.task.stats.rows is not the number of rows of the resource (contrary to resource.stats), but the number of rows processed during the validation, which may be different, e.g if the maximum number of error is reached.

The documentation could therefore be improved.