We must build a directory tree structure corresponding to the files in
the .apk, and use that then in lo_apk_opendir()/readdir().

We can't just return the same subdirectory once for each time we come
across an entry that has it as a prefix in the zip directory.

Use the BSD-licensed "uthash" library (just one .h file actually) from
http://uthash.sourceforge.net/ .