Add data sanitization docs and don't reference Sanitize.

Sanitize is deprecated and was a bad idea. Give some docs/help on where
to find the features Sanitize used to provide but with a stronger
implementation.
Update links.

Link to things that actually exist.
Re-order TOC to be alphabetical.
Update RSS docs to not refer to Sanitize.
Remove additional references to Sanitize.

Show how to use db->value() instead of Sanitize.
Update Model::query() docs

Don't reference Sanitize anymore.
Merge pull request #688 from cakephp/sanitize-docs

Sanitize docs