Update versions and release notes

OData 5..0.0

Update release notes for 4.2.0 release

OData 5.0.0 RC 2

OData 5.0.0 RC 1

Update OData to support .NET Core 3.1

Enable global $count query option (even though it shouldn't be needed…

…). Related to dotnet#567.

Remove obsolete UseQualifiedOperationNames property

Update read me

Describe should be virtual