There should be a standard library method for 'get all the required modules for a given module'

Right now, folks have to write their own version of this analysis that looks like:
```
function dependson(src : string)
    local mod = parse(src)
    local requires = query(mod, function(req). return resolveRequire(req.path) end)
   return requires
end
```

We could just provide this for folks to use out of the box.