Illustrates how to embed Beaker cache functionality within
the Query object, allowing full cache control as well as the
ability to pull "lazy loaded" attributes from long term cache 
as well.

In this demo, the following techniques are illustrated:

  * Using custom subclasses of Query
  * Basic technique of circumventing Query to pull from a 
    custom cache source instead of the database.
  * Rudimental caching with Beaker, using "regions" which allow
    global control over a fixed set of configurations.
  * Using custom MapperOption objects to configure options on 
    a Query, including the ability to invoke the options 
    deep within an object graph when lazy loads occur.

To run, both SQLAlchemy and Beaker (1.4 or greater) must be
installed or on the current PYTHONPATH. The demo will create a local
directory for datafiles, insert initial data, and run. Running the
demo a second time will utilize the cache files already present, and
exactly one SQL statement against two tables will be emitted - the
displayed result however will utilize dozens of lazyloads that all
pull from cache.

Three endpoint scripts, in order of complexity, are run as follows:

   python examples/beaker_caching/helloworld.py

   python examples/beaker_caching/relation_caching.py

   python examples/beaker_caching/advanced.py

   python examples/beaker_caching/local_session_caching.py


Listing of files:

__init__.py - Establish data / cache file paths, and configurations, 
bootstrap fixture data if necessary.

meta.py - Represent persistence structures which allow the usage of
Beaker caching with SQLAlchemy.  Introduces a query option called
FromCache.

model.py - The datamodel, which represents Person that has multiple
Address objects, each with PostalCode, City, Country

fixture_data.py - creates demo PostalCode, Address, Person objects
in the database.

helloworld.py - the basic idea.

relation_caching.py - Illustrates how to add cache options on
relation endpoints, so that lazyloads load from cache.

advanced.py - Further examples of how to use FromCache.  Combines
techniques from the first two scripts.

local_session_caching.py - Grok everything so far ?   This example
creates a new Beaker container that will persist data in a dictionary
which is local to the current session.   remove() the session
and the cache is gone.