Memstate Versions Save

• Update to latest nuget packages
• Update from .NET Core 3 to .NET 6 (libs are still .NET Standard 2.x)
• Drop Postgres Storage module - The module used NOTIFY/LISTEN but we never managed to pass all the concurrency tests
• Drop SqlStreamStore module - We are building a new RDBMS storage module tailored to perform well with memstate. In the meantime, the Memstate.SqlStreamStore 0.7.x nuget package should work fine.
• Drop the pravega storage module - not enough demand to warrant maintenance effort

This release fixes a bug that caused the Engine to fail after executing a command that throws exceptions.

• Internalized Liblog library so it does not show up as a transitive nuget dependency

• Updated to latest nuget dependencies
• Added SqlStreamStore configuration support

Fixes a NullReferenceException bug when raising events from a command that is not run by the Engine, for example in automated tests.

Alpha release for evaluation, not stable! The API is subject to change.