Renaming the main branch.

[JeanKossaifi]

Happy new year all!

To start 2021 right, I have changed the name of the main branch to main, following Github's new convention [why?]. This is already the name we use in the other (newer) repositories in the TensorLy organization but I was worried of the effect this could have on open Pull-Requests. Turns out Github is clever in dealing with the change so the impact should be minimal.

To reflect the change in your local repository:

git branch -m master main
git fetch origin
git branch -u origin/main main

Let us know if you encounter any issue due to the change!