Create on-demand caching that can easily be enabled

Hi,

Please create on-demand caching (versus caching everything). In most ORM's it is quite difficult to add a comment in the query, so I would prefer to use proxy-session variables:

SET PROXY cache_enabled=1;
SET PROXY cache_soft_ttl=3600;
SET PROXY cache_hard_ttl=3630;

This provides functionality for a couple of use cases:

• 90% of the queries are not cacheable and in any case cheap to execute
• Some queries are safe to cache for a minute, other queries are safe to cache for a day or a month

Please make this work out of the box by just adding 'filter=ondemandcache' (or however you want to call it) to router config, optionally setting default ttl's but with a sane default built in as well (5 minutes / 5 minuets + 30 seconds?). Please also add filter=ondemandcache in the example config as (I suppose?) the extra expense for checking a 'SET PROXY' command is very small. If you start to use SET PROXY for other settings it would need to be checked anyways.

Thank you,
Michaël