ManPageGenerator does not ignore "hidden" options

I was expecting the ManPageGenerator to ignore "hidden" options the same way that the standard `--help` renderer ignores them, for example:

```java
@Option(names = "--color", hidden = true)
public void setColor(ColorOptions color) { 
  // ...
}
```

This does NOT render when `--help` is used, but it IS rendered to the manpage doc:

```txt
--color=<color>
```
