Reacting to Roslyn changes
Update Ix-Async pacakge
Making the EntityType API more consitent:
 1. Adding missing methods
 2. Using the same parameters for all methods operating on a specific metadata type.
 3. Adding missing return CanBeNull annotations
 4. Ensuring the uniqueness of the metadata items
 5. Providing more helpfull exceptions
 6. Treating the primary key as a key in TryGetKey and related methods