Example:

Ok with -h (although there could be more context of what the option belongs to):
```
$ MP4Box -h dv-profile
:dv-profile (int):             S set the Dolby Vision profile
```

Broken with -hx:
```
$ MP4Box -hx dv-profile
Possible options mentionning `dv-profile`:
```

```gpac``` broken with -h:
```
$ gpac -h dv-profile
Failed to load filter dv-profile: no such filter registry
No such filter "dv-profile"
Closest filter names: 
- vflip
```

```gpac``` broken with -hx:
```
$ gpac -hx dv-profile
Failed to load filter dv-profile: no such filter registry
No such filter "dv-profile"
Closest filter names: 
- vflip
```

improve help about options
This is a GitHub Issue
repo:gpac
owner:gpac
Title : improve help about options
Issue date:

--- start body ---
Example:

Ok with -h (although there could be more context of what the option belongs to):
```
$ MP4Box -h dv-profile
:dv-profile (int):             S set the Dolby Vision profile
```

Broken with -hx:
```
$ MP4Box -hx dv-profile
Possible options mentionning `dv-profile`:
```

```gpac``` broken with -h:
```
$ gpac -h dv-profile
Failed to load filter dv-profile: no such filter registry
No such filter "dv-profile"
Closest filter names: 
- vflip
```

```gpac``` broken with -hx:
```
$ gpac -hx dv-profile
Failed to load filter dv-profile: no such filter registry
No such filter "dv-profile"
Closest filter names: 
- vflip
```

--- end body ---
