Twisted BCs

Hi Colin,

I was excited to hear about this code from John in Grenada.

Are there any plans to include twisted boundary conditions in this code?  From looking at [Briceño, Davoudi, Luu, and Savage (arXiv:1311.7686)](https://arxiv.org/abs/1311.7686) I don't think it requires too much additional machinery.

Cheers,

Evan