idea: display which features i can change via --features

[brson]

While looking through another manifest file to find the features of a crate I was working on, I wished that cargo would show me it on the command line, along with their definitions.

I would like to be able to see a list of all the features I can modify from the cargo check --features= commands. That includes the crates in the workspace, and some number of their direct dependencies.

It would be more convenient than looking in the manifest, and it can tell you things you didn't know about the dependencies.