Started work on <http://git-annex.branchable.com/todo/to_and_from_multiple_remotes/>.
It's going slow, I had to start with a large refactoring. So far, option
parsing is working, and a few commands are almost working, but concurrency
is not working right, and concurrency is the main reason to want to support
this (along with remote groups).

Today's work was supported by Jake Vosloo [on Patreon](https://patreon.com/joeyh).