Added C-function for faster "editPed"

"pedigreemm" is a great package and I love its speed ... with one exception:
The R-function "editPed" adds missing individuals to the pedigree and orders is according to generations.
This is achieved by a recursive function directly in R. On my dataset with 500 thousand individuals it took several hours to finish. Therefor I added a C-function that does the calculation of the generations recursively.
Now it takes some seconds to finish. Please consider adding it your great package!

Best regards,

Claas Heuer