git_fetch_concurrenty 0.0.2

Do `git fetch -p && git gc` in each sub directory concurrently.
Builds

git_fetch_concurrenty's sandbox limits

All the builds on docs.rs are executed inside a sandbox with limited resources. The limits for this crate are the following:

Available RAM 6.44 GB
Maximum rustdoc execution time 15m
Maximum size of a build log 102.4 kB
Network access blocked
Maximum number of build targets 10

If a build fails because it hit one of those limits please open an issue to get them increased.