Plugs can use a lookup macro.

A plug can have the following form:

    {{!lookup|key}}

and it will be replaced by the key's value
according to the metadata lookup algorithm.
[init] depend on formidable
Fix to issue #158: this.driver is not defined for the path '/'.
Plug: plug=none on a directory.

Fixes #134 and #147.

It implements the behaviour specified in #147.
Requesting a directory with no plugs returns a newline-separated list of entry
names.