Adding initial cache adapter base class.
Updating cache adapters to use base class.

- Remove inherited methods where possible.

Any custom adapters implemented in userland should
be changed to inherit from the new base class as a form
of good practice. However current implementations will
continue to work, thus this doesn't break BC.
Updating cache namespace docblocks.

- Roughly equal structure for all cache adapter docblocks
  to make them easily comparable.

- Documenting atomicity not in general (just hint) but
  on each adapter as this differs from adapter to adapter.

- Adding documentation what adapters should/can/must
  in adapter base class.

- Adding links using tags.

- Removing 'method non-filterable' from cache docblocks.

- Updating enabled mehtod docblocks, equalizing.

- Adding ref to base adapter.
Implementing cache key scoping.

This allows to provide a `scope` on a per adapter
configuration basis. Namespacing/scoping of the keys
is then handled by the adapters transparently.

When multiple apps access the same cache store, scoping
can be used to prevent accidental overwriting of keys.

- Removing unused cache prefix option.
- Adding scoping docs to cache class.
- Adding helper methods to base adapter.
- Adding tests.
Merge pull request #1067 from davidpersson/cache-scoping

Implementing cache key scoping.
Expanding docblocks for cache clear methods.
Return false if cache file adapter clear method fails.
Prevent file cache adapter clear method from going recursive.
Implementing GC for cache file adapter.
Documenting options on cache methods.
Updating docblock for cache clean method.
Fixing formatting in docblocks for respondsTo.

Slightly refactoring Redis::respondsTo().
Delegate method calls to memcached connection object.

Adding tests.
Updating delegation docs in redis adapter.
Harmonizing and formmatting cache adapter constructor docs.
Removing support for strategies with cache delete.
Moving filtering from cache adapters into manager.

Functionality should not be needed to repeated in adapters and
handled by the manager class if possible.

Also adapter methods themselves were never filterable on the
adapter classes. It was always (parts of) the manager class'
methods that were filterable.

That's why filters already in use with the cache manager class
will continue to work as is.

- Updating docblocks.
- Updating and cleaning up all relevant tests.
- Make read/write/delete/increment/decrement methods to not
  return closures anymore.

BC Break: This change requires any cache adapters implemented in
userland to not return closures for read/write/delete/increment/decrement
anymore. Please update your code accordingly.

When using the standard lithium adapters no change ist required
any code will continue to work as is.
Merge pull request #1068 from davidpersson/cache-move-filtering

Cache strategy/filter cleanup
Cleaning up; correcting cache docs for strategies option.
Fixing typo in assertion method.