Remove usage of `AS::Deprecation` and core extensions.
Deprecate support for symbols as the `store` option.

Concrete objects should be passed now on. Any object that
responds to `write` and `read` should work.
Replace `inject` usage with `each_with_object`.
Merge branch 'master' into decouple-active-support
Improve docs a bit.
Add a `DEPRECATION WARNING` prefix to `Kernel.warn` call.
Remove `activesupport` as a runtime dependency.
Merge pull request #33 from plataformatec/decouple-active-support

Decouple ActiveSupport dependency