Introduce GetAll() method

I noticed that there is no 'GetAll()' method for this, as described on this page:

https://docs.microsoft.com/en-us/dotnet/architecture/microservices/microservice-ddd-cqrs-patterns/enumeration-classes-over-enum-types

Could this be added to the base class?

```
///
/// Retrieve all enumerations of the SmartEnum
///
/// new of type
///
public static IEnumerable GetAll() =>
typeof(T).GetFields(System.Reflection.BindingFlags.Public |
System.Reflection.BindingFlags.Static |
System.Reflection.BindingFlags.DeclaredOnly)
.Select(f => f.GetValue(null))
.Cast();
```

This should get all of the static enum values defined

Start by locating the SmartEnum base class and reviewing how its static values are currently represented and tested. Use the proposed GetAll() behavior in the issue as the target: callers should receive all static enum values defined on the concrete type.

Written by the indexing model from the issue text.