chore: Tidy up whitespace in declarations and definitions
fix: Use `png_voidp` instead of `voidp` in pngread.c and pngwrite.c
Bump version to 1.6.54.git
ci: Update the install section for AppVeyor CI
Merge tag 'v1.6.53' into libpng18
Release libpng version 1.6.53
build: Remove leftover ASM language from CMake `project`
build: Remove leftover ASM language from CMake `project`