Module Dependency Graph / Tracing

[dazinator]

Create a Madge pipe, so that netpack can compute dependency graph information. This information could be consumed in #36 by allowing the server to include information about dependent modules when it signals to the browser that a module has changed. This will allow the HMR implementation in the browser to reload not just the changed module but also all dependant modules.

[dazinator]

Opened regarding in memory file processing: pahen/madge#186 (comment)