cargo: dependency-resolution

[graydon]

Cargo packages will depend on other packages. Add dependency-graph-resolving logic and recursive dependency-installation. Dependencies can be expressed in the central json file. Cyclic dependency is an error condition.

Also differentiate which installed packages are installed as actually-requested targets vs. simple dependency-satisfying ones, and give cargo the ability to purge/gc packages that were installed only as dependencies and are no longer referenced by "requested" packages.

[brson]

Cargo now resolves dependencies by directly parsing the use statements - there's no external database of dependencies. It doesn't do an GC of unused packages.

[z0w0]

Closing because Cargo is obsolete as of version 0.6.