jQuery plugin for parsing metadata from elements

 Sets the type of metadata to use. Metadata is encoded in JSON, and each
 property in the JSON will become a property of the element itself.
 .
 There are three supported types of metadata storage:
 .
   attr: Inside an attribute. The name parameter indicates *which* attribute.
 .
   class: Inside the class attribute, wrapped in curly braces: { }
 .
   elem: Inside a child element (e.g. a script tag). The name parameter
          indicates *which* element.
 .
 The metadata for an element is loaded the first time the element is accessed
 via jQuery.
 .
 As a result, you can define the metadata type, use $(expr) to load the metadata
 into the elements matched by expr, then redefine the metadata type and run
 another $(expr) for other elements.