Render function cache within HTTP pipeline

[tokrug]

As of now there is only one type of cache available which checks if the original HTML for a given path has changed or not. If it did then the new HTML is transformed into a render function and stored for future requests.

While it does save some time spent on parsing the HTML which does not change most of the time, an HTTP request is still executed on every pipeline call.

Introduce a new cache specific to the HTTP pipeline that would use headers and other HTTP data in addition to the request page path as the cache key.