sync man page with changes 1.2.3 -> 1.2.11. some changes:

sync man page with changes 1.2.3 -> 1.2.11. some changes:

- update references version number
- Z_NULL -> NULL; from millert
- terminate function synopses in main body with ";"; from tb
- NULL -> NUL; from tb
- update NAME and SYNOPSIS for added functions
- updated copyright, to match zlib.h
- simplify \-1 -> -1

ok tb