Added a missing function for POutput.
Implemented parse_rtol_bit, which is necessary for zLib.
First implementation of zLib.
Moved the parse_rtol_bits implementation back to parsifal.

As this RTOL bit parsing madness is also present in ZLib structures, we might need it elsewhere.
There is also an incomplete version of rtol_bit_int and rtol_bit_bool in BasePTypes.
Rewrote zLib.ml to distinguish between raw DEFLATE (RFC 1951) and zLib (RFC 1950).

RFC1951 is correctly implemented.
zLib.ml lacks a real dump function, and some fields are not correctly taken into account for the moment.
The RFC1950 has been added to the repo.
Changed the way lists are displayed.
Implemented most of PNG chunks.
Updated AUTHORS.
Commented on PNG implementation.
Improved image_time chunk display.
Added a relevant exit code to test_png.
Updated TODO.