unarr: stop requiring a patched zlib for Deflate64 support (not much of a speed difference, since the Deflate64 patch to zlib disabled inflate_fast)
make Canvas.cpp to compile as stand-alone
move OnDropFiles into Canvas.cpp
move delta-per-line logic into Canvas.cpp
unarr: merge fast and non-fast inflate code paths
unarr: further clean up inflate.c