Updating cache adapters to use base class.

- Remove inherited methods where possible.
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.

- Removing unused cache prefix option.
- Adding scoping docs to cache class.
- Adding helper methods to base adapter.
- Adding tests.