Use separate options for enum values

Having support for `enum` flags is great! But sometimes you don't want the user to use the actual enum values. In fact, they could easily be re-factored causing breaking changes for existing command line integrations.

It would be nice if you could specify names which would then be used instead of the enum values. E.g. using the [DisplayAttribute](https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.displayattribute?view=net-6.0).

```c#
[Flags]
public enum MyEnum
{
None = 0,
[Display(Name = "a")]
VeryLongEnumValueNameHere = 1,
[Display(Name = "b")]
EvenLongerEnumValueNameHereWithNoRiskForTypos = 2,
[Display(Name = "c")]
WouldBeNiceWithShorterName = 4
}
```

The corresponding command line could look like this: `foo.exe --my-enum-value a|b|c`

Or even better...

**Allow OptionAttribute on enum values?**
We could allow the `OptionAttribute` on enum values and get separate arguments for each enum flag:
`foo.exe -a -b -c`

```c#
[Flags]
public enum MyEnum
{
None = 0,
[Option('a', "long-value", HelpText = "Long value")]
VeryLongEnumValueNameHere = 1,
[Option('b', "even-longer-value", HelpText = "Even longer value")]
EvenLongerEnumValueNameHereWithNoRiskForTypos = 2,
[Option('c', "nice", HelpText = "Would be nice")]
WouldBeNiceWithShorterName = 4
}
```

Feasible?