Type aliases are missing description and more

Type aliases are not showing the description and parameters:
```
/** Determine if `T` meets the requirements of @b CompletionHandler.

This trait checks whether a type meets the requirements for a completion
handler, and is also callable with the specified signature.
Metafunctions are used to perform compile time checking of template
types. This type will be `std::true_type` if `T` meets the requirements,
else the type will be `std::false_type`.

@par Example

Use with `static_assert`:

@code
struct handler
{
void operator()(error_code&);
};

static_assert(is_completion_handler::value,
"Not a completion handler");
@endcode
*/
template
using is_completion_handler = std::integral_constant;
```

Is only showing the brief and synopsis