resource: escape slashes from download_name

This is useful to be able to write go resources using their package
name as the resource name
Add Go language module, resources

This introduces a new GoResource category of resource. GoResources
have a specialized stage method which allows a resource to stage
itself into a gopath.

The new Go language module provides a one-liner to stage all
GoResources present in the formula.
mpdviz: model deps as resources
mpdviz: add 0.4.3 bottle.