cargo metadata's resolve output doesn't specify depenency kinds

[sfackler]

cargo-tree needs to know the kind of dependencies (i.e. normal, build, dev) before it can switch over to using cargo metadata rather than linking to cargo as a library.

[alexcrichton]

This seems reasonable to me! Serialization currently happens here and we'd probably just tweak the dependencies list slightly in Node

[sfackler]

Seems like this'd require a metadata version bump, right?

[matklad]

Seems like this'd require a metadata version bump, right?

Adding new keys doesn't need a version bump, the clients should ignore extra keys.

[alexcrichton]

Ah yeah I think it may require some intrusive code changes, but I figured we could just add keys to the maps emitted.