wad_index.ini: Renamed 'index' to 'files'

- The table 'index' conflicted with the SQLite keyword 'index'
wad_index.ini: fix missing semicolon in 'wads' SQL
wadindex/ZipTool.pm: close #84; Use File::Temp for temp dir

- For Linux, use /dev/shm for a temp dir if it exists, otherwise, use
  the builtin "hints" in File::Temp