Group constraints classes and type aliases together

[Iltotore]

To better organize the API documentation, especially for io.github.iltotore.iron.constraint.xxx objects, constraints should be grouped together, no matter if they're defined using a type alias (e.g Positive) or a final class (e.g Greater).

-- Constraints
final class Greater
type GreaterEqual
type Positive
...

instead of

-- Classes
final class Greater
...

-- Types
GreaterEqual
Positive
...

This can be done using @group, @groupname and @groupprio. See Ciris' ConfigValue for example.