...because I don't like semver::VersionReq.
Add this to your Cargo.toml:
[dependencies]
# ...snip
# you'll probably want to use versions if you're using version
# constraints
semver = "0.9"
# the actual constraints library
semver_constraints = "0.1"
# if you want to use serde:
# semver_constraints = { version = "0.1", features = ["serde"] }See the crate docs for motivation and info on the API.
semver_constraints is distributed under the MIT License.