fix grayscale image decoding
save to jpg format
try looking for model files from executable directory
add cmake option to build with system libncnn and libwebp
update ncnn for faster gpu loading
multi-gpu support

webp encoding
fix black or noise output on windows

pre-compiled binary for windows / ubuntu / macos 64bit

build with ncnn 20200530

online spirv compilation, much smaller executable binary
link with static msvc runtime
webp image decoding
properly handle images with alpha channel
reduce gpu memory usage
automatic tilesize settings according to the current gpu heap budget
github action ci added