Plugin specific options

[mwestphal]

Is your feature request related to a problem? Please describe. In F3D, we can load plugins that provides readers and importers. However, certain file formats have specific options that we currently cannot control. eg: USD as "purpose" concept. VDB has a "resolution" concept in its VTK implementation.

Being able to control that some way or another would be practical, it means being able to dynamically declare options in plugins.

Describe the solution you'd like

• Add a mechanism that let plugins declare new libf3d options, eg plugin.vdb.resolution
• Add a generic "define" CLI options similar to cmake that let CLI user specify the option, eg : -Dplugin.vdb.resolution=10