It can be difficult to understand why a given module is a part of our Go
dependencies. This change adds utility scripts--inspired by Rust's
`cargo tree`--that use `go mod graph` to inspect Go dependencies.
* `go-mod-tree` -- like `cargo tree`, prints all dependencies from an
optional root module.
* `go-mod-versions` -- enumerates all versions of a module in the Go
dependency graph
* `go-mod-why` -- like `cargo tree -i`, prints the tree of modules that
depend on a given module.
Signed-off-by: Oliver Gould <ver@buoyant.io>
Oliver Gould