I think that the Apache 2.0 license has some significant advantages over the BSD license, namely that patents are explicitly dealt with and clause 5 makes it explicit that contributions to the main repo will be licensed under Apache 2.0 unless otherwise specified. We still need to keep BSD license around for anyone who has not agreed to relicense, but since Apache and BSD are compatible, it's not a problem for all work going forward to be under the Apache 2.0 license.

As part of this, I think we should also add an AUTHORS file, so that the copyright notice is more accurate. I'll compile an AUTHORS file and it will be explicit who has their contributions licensed under the old BSD license and who has their contributions licensed under Apache 2.0, and any author on the list can make a PR to add themselves to the Apache 2.0 relicense file. If we get to 100%, we'll drop the old BSD file.