IMPORT: slz: update slz to version 1.3.0

IMPORT: slz: update slz to version 1.3.0

This version provides the uslz (u stands for uncompress) API that allows
to decompress zlib/gzip compatible streams (including the ones generated
by slz) using 32K sliding buffer. It is meant for users that care about
memory footprint, but if performance is the only priority, using zlib is
perfectly fine for this.

Credits to Andrew Church <achurch@achurch.org> for providing
https://achurch.org/tinflate.c aka tiny inflate library as public domain.
libslz decompression implementation was greatly inspired from tinflate
library by Andrew Church.

zdec utility was updated to leverage this new API in order to act as a
fully operationnal decompression tool instead of simply dumping basic
debug infos like it used to do.

Shortlog:

Aurelien DARRAGON (5):
        REORG: move generic internal function and helpers inside slz-prv.h file
        MAJOR: reorganize libslz to split compression API code from common API code
        MAJOR: slz: implement uncompress API (uslz)
        REORG: rename zdec utility to zdecode
        MINOR: add zdec decompression utility

This is libslz upstream commit 5a002417e1c3706c8cc835767e5f7b02c6ea5078