Removed non-functional links.
Removed links to API documentation.
Removed link to Rails 2 material.

Renamed "References" to "Further Reading".

These plugins are obsolete even for Rails 2, they have no place in a Rails 3 guide.
Also removed "mad cool" reference.

If anyone has ideas about cache plugins that *must* be included, I would love to know.
As far as I am concerned the rails guides should stick to built-in methods and have a
simple list of references for people wishing to investigate further.

I will check out the references after this commit to see if they're up to date.

Caching guide: documents that page/action caching run in an after_filter, and this spurious cache entries are avoided just by halting the request

bring index actions back in caching guide, REST conventions are encouraged and surrounding text assumes index