Support legacy ZIP compression methods (for decompression at least)

libarchive and zlib don't support legacy (pre-DEFLATED) ZIP compression methods (in particular, the "implode" method - method #6 (closed)). But it can be done:

https://www.hanshq.net/zip2.html https://github.com/jsummers/oldunzip/

This would allow the extraction and viewing or subsequent download of archived files from legacy ZIP files.

Whether this is done as a patch to zlib or libarchive or something internal to sbbs, it seems totally doable.