Proposal: trap init functions

Currently init functions are skipped, that makes it impossible to inject mock and collect trace during the init stage.

However since init functions just run once and run serially, it has no performance impact at all. It might be useful.

At least allow to trace package initialization traces. This can be done by simply inserting an init function in each package, and emit a print statement.

And maybe xgo can provide a tool called xgo inspect check-init, when invoked will do a static analysis to recursively find all imports and render the import tree in a web UI.

A successor of https://github.com/xhd2015/go-inspect/tree/master/cmd/depcheck