Put `ffm-plus` into a separate GitHub repository

[chuigda]

So we can maintain their versioning, publishing and change log separately.

Blocking factors:

• Implement ISharedLibrary/ILibraryLoader #110 (Resolves LWJGL-alike SharedLibrary interface implementation, reducing "global" System.load/System.loadLibrary #91)
• Find out how to link to ffm-plus JavaDoc after making separation.