[patch] decorator for managing cache-control header

[hugo]

The attached patch is a decorator that allows management of the Cache-Control header for django views. The idea is to tag all views that contain sensible data with:

Error: Failed to load processor private

No macro or processor named 'private' found

That way a Cache-Control: private header will be generated. This decorator merges the cache-control value with already set values and the patch changes the caching utilities to use this merging technique, too.

I patched the documentation to contain a short chapter on the cache_control decorator, too.