z3 egg improvements

[Jim Ursetto]

z3 implements RFC1951 (deflate) and RFC1952 (gzip) but not RFC1950 (zlib), which is basically deflate + a header and adler32 checksum. zlib format is used by some applications in lieu of a raw deflate stream -- for example, git objects are stored in this format. The default python and ruby zlib compression functions read and write zlib format as well, relegating raw deflate to second class status. That's probably because this is the standard behavior of libz itself, but support seems warranted.

Also as in closed ticket #82, the interface should be improved to be more agnostic to input or output source, allowing any format to be read or written to a port or string. Backward compatibility should be retained where possible.