#12 Allow use of Cache out of Web Addressable space

[KosherJava]

The current caching mechanism used by FeedCreator saves teh file in a web addressable dir and redirects the call to that file. Many servers do not want any web addressable space to be writable, so the caching should be able to read (I believe that it can currently write to anywhere in the file system, but the redirect will fail) the cache from any file location and buffer the output back to the user. While not as efficient as a redirect, is is certainly cheaper than regenerating the feed. For PhpGedView we will likely have to use our own caching mechanism, because the feed can be generated in multiple languages, and a different cache dir for each GEDCOM (genealogy file). Such caching would not be of general interest to FeedCreator users. One thing that would be nice of a caching mechanism, would be the ability to cache entries individually. Some entries are static and can be cached, but others such as a random image entry, would not be static, and that specific entry should be generated on the fly.