Nebulex v3.0.0-rc.2 roadmap

[cabol]

Nebulex v3.0.0-rc.2

• Add docs and examples of Nebulex.Adapter.Observable to the "Getting Started" guide.
• Update Nebulex examples to use v3.
• Implement nebulex_mnesia adapter. This new adapter will cover several use cases as well as distributed cache topologies. With Mnesia, it will be possible to have a local cache and a distributed cache with replication (and fragmentation). Maybe deprecate Nebulex.Adapters.Replicated adapter.