The identity factory must not crash when a compatible identity value is used

[craigfowler]

Currently, the identity factory requires an identity value to be an exact type match for the desired identity value.

For example, of an entity requires Int64, then an identity cannot be created using an Int32, even though it is compatible/has an implicit cast available. This ticket is to relax that restriction so that compatible types may be used.

Sample exception & stack trace

System.ArgumentException : Identity type `Int64' was specified but provided identity value was a `System.Int32'.
Parameter name: identityValue
  at CSF.Entities.IdentityFactory.Create (System.Type entityType, System.Type identityType, System.Object identityValue)
  at CSF.Entities.Identity.Create[TEntity] (System.Object identityValue)