Hook up crates feed via cargo

[tom--pollard]

Targeting a rust:minimal container for cargo builds of the given package tarballs for example

[tom--pollard]

The crates api exposes https://crates.io/api/v1/crates/$package_name/$package_version/download (values of which exist on the Package{} structs) which provides the given source tarball via wget, for example. This could then be extracted and installed with cargo build during the analysis phase under falco

[calebbrown]

This is done.

#551 is logged to add import support.