Squash rust repo to make it fast to download

[roblabla]

We should have a rust repo with the whole history squashed to one commit, so that downloading it with Xargo is instantaneous.

[kitlith]

Why not make Xargo git clone --depth=1?

[roblabla]

I think (but would need to check) that xargo just uses cargo? So it might be cargo that needs to do that. If it doesn't already.

[justgerd]

last time I checked this wasn't possible.

we'd also need to flatten the repo (remove submodules) or fork those & squash them too

[kitlith]

right, there's an issue on cargo: rust-lang/cargo#1171

which is blocked on an issue in libgit2....

[roblabla]

for reference (took me a while to find it), the libgit2 issue: libgit2/libgit2#3058