Sort crates within a category by downloads by default
Sort crates within a category by downloads by default

There will be an RFC soon about whether this is the best ordering or
not.

steveklabnik/crates.io,steveklabnik/crates.io,Susurrus/crates.io,Susurrus/crates.io,steveklabnik/crates.io,Susurrus/crates.io,rust-lang/crates.io,rust-lang/crates.io,steveklabnik/crates.io,rust-lang/crates.io,rust-lang/crates.io,Susurrus/crates.io