Multiple instances when opening from the Windows explorer

[Meakk]

Describe the bug
When opening several files from Windows explorer, one instance per file is opened.

To Reproduce
Steps to reproduce the behavior:

1. Select several files
2. Right Click -> Open
3. Multiple instances are opened

Expected behavior
Only one instance of F3D in multi-file mode should be opened

System Information:

• OS: Windows
• GPU and GPU driver: Irrelevant

F3D Information
Paste the content of f3d --version: 1.3.1

Additional context
We probably need to extend our shell extension for that: https://stackoverflow.com/questions/27088510/implement-explorer-contextmenu-and-pass-multiple-files-to-one-program-instance

[mwestphal]

FYI @jpouderoux

BTW @Meakk , there is the same "issue" on any file explorer on linux or MacOS.