@Typedef parsing fix & improvement

[obiot]

1. optional tag missing

When using typedef, optional properties are not referresed as such in the generated documentation:

https://github.com/melonjs/melonJS/blob/eb0a08fbd253883b2a2dc77a9de04ebde52ac336/src/loader/loader.js#L103-L113

becomes :
https://melonjs.github.io/melonJS/docs/melonjs/loader/Asset.html#type

2. property list

list of defined properties for typedef is not coherent with how properties are displayed/generated when not using typedef

see here for example (an object defining properties) :
https://melonjs.github.io/melonJS/docs/melonjs/utils.html#getUriFragment

compared again to (typedef defining properties)
https://melonjs.github.io/melonJS/docs/melonjs/loader/Asset.html#type