Update to Microsoft.Bcl.Async 1.0.14-rc
IObservable isn't covariant on WP7
Update to Rx 2.1.30204.0
WP8 doesn't need shims anymore
Circular dependency is too circular, we need to put AkavacheDriver somewhere else
Update NuSpec dependencies to Rx 2.1
Merge pull request #171 from reactiveui/upgrade-packages

Upgrade Rx and Microsoft.Bcl.Async