Move to BSD license

[duncanmmacleod]

I would like to consider moving gwpy to a BSD-style license, away from GPL, mainly after reading this post from John Hunter (creator of Matplotlib).

cc @gwpy/gwpy-developers

[duncanmmacleod]

It's unclear to me whether this is even possible, given that a number of our dependencies are GPL-licensed.

[alurban]

@duncanmmacleod, John's argument is pretty convincing, maybe this is something we should look into?

[jrollins]

I don't have any particular problem with BSD licenses, but I'm not necessarily convinced by this argument. I doubt that gwpy is losing much "mind share" from the private sector.

Also, this point begs the question:

There is a lot of GPLd code in the world, and it is a constant reality in the development of matplotlib that when we want to reuse some algorithm, we have to go on a hunt for a non-GPLd version.

The reason they have to go on the hunt for non-GPL code is because they made their code non-GPL. So that's not some inherent problem with GPL code.