Add Cargo.lock file

[samford]

In the process of making changes to formulae in the Homebrew package manager, I noticed that dssim was one of a handful of Rust binary projects without a Cargo.lock file in version control. The Cargo book recommends the following (source):

If you’re building an end product, which are executable like command-line tool or an application, or a system library with crate-type of staticlib or cdylib, check Cargo.lock into git.

More information about the reasoning can be found in the "Why do binaries have Cargo.lock in version control, but not libraries?" section of the Cargo FAQ.

The Cargo.lock file helps package managers to keep builds reproducible, since cargo install simply uses the latest dependency versions unless the --locked flag is added to the command, in which case it will use the versions outlined in Cargo.lock. Without a Cargo.lock file, there's a chance that a dependency update will break the build sometime in the future, which is something I've already encountered with other Rust binary projects.

Would you please consider checking Cargo.lock into version control?