Fix num_colors exceeding amount of colors in palette leading to use of uninitialized colors
Handle png -> pal conversion (aka extracting JASC palettes from png
Allow using only file extension as output to reuse entire path from input before extension
The compiler flag -s is not necessary and causes build failure on some
systems (macOS, clang compilers) due to it being deprecated.
Additionally, on those same systems, tools/aif2pcm/main.c failed to
compile due to an overly cautious compiler not liking some struct
declarations.
These changes afaik do not affect other builds.
