Add ahnen_parents function to take an array and produce an Ahnentafel number

[yewtc]

Given an array of strings like ("Father, "Grand Mother","Great Grand Mother", ...), the ahnen_parents function

Creates the Ahnentafel appropriate number . In pratice it matches on/Mother/iin the string, so all else if noise.

[coveralls]

Coverage: 100.0%. Remained the same when pulling aabf4d1 on yewtc:ahnen_parents into 235b7a8 on davorg:master.

[davorg]

Hi Steve,

This looks useful, but could you change it to use the parent_names class attribute? That way it would continue to work if someone subclasses the module to support a different language.