I was getting a compilation error (something in the latest Rust
compiler?), related to a nom dependency (bitvec v0.19), but nom 7 does
not depend on bitvec by default anymore, yay!
The move + clone closures feel kind of wrong though
Unfortunately cargo doesn't allow optional dev dependencies (see
rust-lang/cargo#1596) so this is the workaround.
Previously, running `cargo test` triggered the build of all dev
dependencies, including criterion, which in turn pulls in a lot of
stuff. Running tests should be faster, hence this change.