Circling drain for final V2 release

Thanks to @ameier38 @AndrewRublyov @asetda @DSilence @eiriktsarpalis @jakzale @jgardella @Kelvin4702 @Rajivhost @Szer for notable contributions since 1.x

The V2 code is complete and resilient, with no known issues or planned hardening work.

However, we're not actually baking a 2.0.0 non-preview release until the last responsible moment which will be before 20 March, 2020 - the next geo-equinox.

See CHANGELOG.

Some notable highlights:

Core

• The Cache type and related ICache interface now lives in Equinox.Core rather than being store-specific 🙏 @DSilence
• Stream now admits an optional 'Context to facilitate correlationId/causationId wiring
• Stream now admits a ResolverOption.AllowStale to facilitate stale/optimistic cached reads
• FsCodec repository now hosts IEventCodec interface, StreamName helper and concrete serializer bindings
• Various items exposed and polished for usage from Propulsion and dotnet-templates
• new Propulsion repository now hosts Projection Streaming / Feed management logic that has rested in here in recent times
• new eqx dump supports dumping events and/or [decompressed] snapshots to the screen

NEW SqlStreamStore support

• 🙏 @Rajivhost

Cosmos

• Interoperable with v1 storage formats - i.e. it's intended to be safe to use 1.x and 2.x libs in any combination
• Added RollingState and Custom modes, enabling one to use event sourcing facilities to manage a single rolling document state efficiently
• Renaming (using Cosmos SDK terms from V3, i.e. Collection -> Container) and medium density renamespacing hence v2
• eqx init supports updating RU allocations, and database level assignments
• new eqx stats dumps event counts for Cosmos