Export to and import from updog

[lvclark]

It would be nice to have some convenience functions to convert between a RADdata object and the input and output of updog. This would allow users to take advantage of the file import and export options in polyRAD, while performing the genotype calling itself in updog (more accurate than polyRAD in some cases but much slower).

If you would like to add this feature and make a pull request, just comment here and I will give any help and guidance that I can. In particular see the multidog and format_multidog functions in updog. See also the checklist for pull requests.