Crates should have the file extension .crate not .tar.gz. There is no guarantee it will stay in the same format in the future. It is also what their original name was according to file(1):
```
$ file rust/crates/*
rust/crates/better-panic-0.2.0.tar.gz:gzip compressed data, was "better-panic-0.2.0.crate"
rust/crates/binary-space-partition-0.1.2.tar.gz:gzip compressed data, was "binary-space-partition-0.1.2.crate"
```
This change touches many files which are updated very regularly. I already had to rebase it multiple times. I will land this real soon because of this. Let's say on Saturday. I am opening this review in case somebody has time to sanity check what I did here.