Manu/Navigation helper functions

[mvlcek]

(I' really like a standard way of caching all of the menu data as an XML file to get into the core rather than various plugins all doing variations of the same things, such as the i18n, the multilevel menu plugin, the pagecache plugin, etc.)

In this case all meta data (including additional fields included by e.g. the Custom Field plugin) of the pages must be included in the cache, i.e. everything but the content.
if everything is accessible in an array indexed by slug, whose values are arrays with the meta data (values indexed by the names), this would be really useful.