Move to pwntools Github organization

Gallopsled was a merger between the [Pwnies.dk](https://pwnies.dk/) and [European Nopsled Team](https://ctftime.org/team/282) for DEF CON 2014, but that died after a few years. @br0ns and @TethysSvensson agreed to move the project to another organization like https://github.com/pwntools. That would make it easier to find and remember. It would also represent the current state of the project being maintained by the community spanning many different CTF teams rather than one.

I haven't looked at the details on Github yet but I'd expect the old Gallopsled repositories to still work and forward to the new location. Does anyone know any problems that you'd have to watch out for?

The issue concerns moving the pwntools repositories from the Gallopsled organization to https://github.com/pwntools. Start by checking GitHub's organization-transfer requirements and whether the old repositories will continue forwarding; done means the migration risks are understood and the transfer plan is agreed.

Written by the indexing model from the issue text.