Add support for GPT

[py-crash]

I will be great if gpart could write GUID Patition Tables. It can recover de partiions from a GPT partitioned disk, however it won't be able to write the table since only admits 3 primary partitions

[baruch]

I do not really have time for active development of gpart, I'd be happy to take a merge request implementing relevant changes though.

[py-crash]

I'm no developer so i cann't help on that. Keep the issue open so maybe someday will be closed. Thanks for the great tool anyway. You saved all my important information.

[q2dg]

Maybe https://github.com/cgsecurity/testdisk is an alternative