Add FFI ZLib library and trader Gzip

[vaisest]

Description of the problem being solved:

In 0.5.5 the trader API was changed slightly. It seems that the old way of using it still works, but as far as I understand, some of the old functonality will be gone in ~1 month. The changes are:

• Short codes were replaced by B64 GZipped JSON. This is similar to the ?q= parameter, with the exception that it only has the query field. I.e. you can't set the sort order with it.
• A GET search endpoint was removed. This is fine since now there's no need to fetch the short code IDs since we can just decode them.
• GZip was implemented by adding a library which has bindings for the ZLib dll we already provide. This also has the added benefit of working with the headless wrapper, which should solve some PoB1 problems as it uses ZLib compressed data (the files called .zip despite not being zip)

Steps taken to verify a working solution:

• Buy similar works
• Unauthorized trader link works
• User-provided url authorized search works
• Authorized search flow works
• Tests updated

[vaisest]

Note that I changed this so that only the PoB zlib is used. Otherwise the file is just https://github.com/hamishforbes/lua-ffi-zlib/blob/master/lib/ffi-zlib.lua