Feature Request: A way to backup/restore cargo install'd crates

Describe the problem you are trying to solve
I use cargo to install some system utilities on my machine. I generally like to back up the installed packages + flags I used to install them to a file that I can use to restore those packages onto new machines. For example, on OS X, brew-bundle supports this, letting you run brew bundle dump to output a file that can be read via brew bundle later to restore this set of installed packages.

Cargo tracks installed crates via the ~/.cargo/.crates.toml file. This seems to be the same file that is read when you run cargo install --list.

Describe the solution you'd like
I'd like to see a cargo install --dump or similar that would output the list of installed crates to stdout, but rather than in a human-readable format, in a json/toml/other structured format.

The companion command would be something like cargo install --dump /path/to/dumpfile.toml, which would cargo install all listed crates with all of their options.

Notes
If this is a desirable feature, I'd be happy to submit a PR adding this functionality.

Thanks in advance for any thoughts!

Start by examining Cargo's handling of ~/.cargo/.crates.toml and the existing cargo install --list entry point. Define how a structured dump represents installed crates and the flags needed for restoration, then verify that the proposed dump and restore flows preserve those options and reproduce the listed installations.