* determine mime-type to use during ffprobe evaluation stage, don't bother rechecking by file extension
* set mjpeg content-type
* fix up tests expecting differing default values
* use single-threaded image resizing in native code so we have more control over goroutines
* implement parallel-free versions of image transform functions also
* remove debug code
* wrap thumbnailing code to handle generation natively where possible
* more code comments!
* add even more code comments!
* add code comments about blurhash generation
* maintain image rotation if contained in exif data
* move rotation before resizing
* ensure pix_fmt actually selected by ffprobe, check for alpha layer with gifs
* use linear instead of nearest-neighbour for resizing
* work with image "orientation" instead of "rotation". use default 75% quality for both webp and jpeg generation
* add header to new file
* use thumb extension when getting thumb mime type
* update test models and tests with new media processing
* add suggested code comments
* add note about thumbnail filter count reducing memory usage
