0.4.5

• introduce nordlicht_generate_step and nordlicht_done to the API, for simple, non-blocking applications
• improve FFmpeg backwards compability down to v3.0 (thanks, Manuel!)
• fix build on ARM platforms
• correctly open files which contain a colon (thanks, Roland!)
• various bug fixes and stability improvements
• tool: when the user specifies a non-PNG file as output, warn them but don't fail