Also added scripts/chkfmt to validate the format of all the files that can
reasonably be validated (it is suggested to run "make distclean" before
checking, because some machine generated files have long lines.)
Reformatted the CHANGES file to be more consistent throughout.
from the source files, along with "#define PNG_EXPOSE_INTERNAL_STRUCTURES"
and "#define PNG_NO_PEDANTIC_WARNINGS" (John Bowler).
Also created new pngdebug.h and moved debug definitions there.
