Add a CachingExecutionFilter

[david]

The name says it all ;)

[david]

See also DavidZuelke?

[david]

Symfony has good caching, too, with conditional get and vary header support etc. This is important, too.

[david]

First version, fully functional already, in changeset:364

[david]

config handlers added in [373]

[david]

(In [594]) moved renderer retrieval to separate getRenderer() method in View, execute() cannot return a renderer anymore now. this is necessary so caching may work later for people who set their output type in the View, and not via filters or the routing. refs #141 and #78

[david]

(In [595]) Action execution in ExecutionFilter? sits in a separate method now, making it easier to extend. refs #78 (in a way)

[david]

(In [1635]) finally: caching. one config file per action, definitions can be specific to one or more request-method, each definition can contain settings specific to one or more output types, groups (like in smarty, multiple sources like string, locale, request param etc), cache TTL ('2 days 4 hours'), caching can be controlled on a per layer level, slots can be included in the cache, action attribs, template vars and request attribs (yes, with namespace) can be restored, restrictable to certain views, closes #78. also did some minor fixes here and there, added slots to sample app.