thirdparty: add zpipe.c from zlib:/examples
zlib: whoops. fix syntax
zlib: rework option parser
zlib: accept file argument as input, for consistency
zlib: add changelog note
Merge branch 'zlib'

Add a 'zlib' tool written in C (basically just examples/zpipe.c from
zlib source tree, with some adjustments). It's faster and does not
depend on Python... but does depend on libz.