Rework convert functions in halide_image_io.h
Rework convert functions in halide_image_io.h

Complete the type-to-type conversion matrix to make implementing Tmp file IO easier.


Former-commit-id: 1781960ee088a6746f49bc55f8e418d972514eff
Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide