r7

• Support all constant input formats (internally clips are converted to float before processing and converted back to their original format afterwards; all subsamplings are supported, but for now, left-aligned chroma is always assumed; the python wrapper is now only needed if you don't want to descale chroma)
• Add a generic Descale filter that takes a string kernel parameter to make it simpler to write wrapper functions
• Add opt parameter to manually select optimizations
• Split the code for the VapourSynth plugin and descale
• Change license to MIT