AddIrregular() "data" -> "data" instead of "datum"

[MJacred]

Though rare, sometimes you have a Table which ends with "Data", like "PlanData".

Currently, this generates PlanDatum, which does not make much sense…

if AddIrregular() is only for singular -> plural, then probably rs.AddSingular("data", "data")

[stephenafamo]

PR welcome