Media configuration helper

• Document that libvlc options start with -- while media options start with :
• Complete EnableHardwareDecoding with Disable.. and add support for other platforms https://code.videolan.org/videolan/LibVLCSharp/blob/master/LibVLCSharp/Shared/Media.cs#L1090
• File caching
• Network caching
• What else?
• Comment all those fluent APIs
• Build() should return a List<string> and calls to AddOption should contain one option.

We plan to keep that helper small and focused on important, major configuration options (like enabling/disabling hardware decoding). More complex cases of configuration, with sout and several options for example, won't be supported with a fluent API. For those, just pass the regular CLI args as strings.

We need to adapt the helper to new libvlc builds if CLI args change.