feat: add support for 'system/' directory

 * Some archives (e.g. 'update-kindle-32.4.6.5_user_465000520.bin') do not contain
   an image, rather a directory with all of 'system' content. Apparenlty,
   this is usual for Android 5.1 and lower archives.

 * As an easy solution, just archive the content of 'system/' and then
   rename it to 'system.img'.

Change-Id: Iea84954c4c143d260c21a017ae9280ecfebe9b73

Author: AntoninoScordino

extractor.sh

@@ -497,6 +497,15 @@ elif 7z l -ba "${romzip}" 2>/dev/null | grep -q "system.sin\|.*system_.*\.sin";
     fi
 elif 7z l -ba "${romzip}" 2>/dev/null | grep -q ".pac$"; then
     unisoc
+elif 7z l -ba "${romzip}" 2>/dev/null | grep -q "system/*"; then
+    echo "[INFO] 'system/' directory detected"
+    7z x -y "${romzip}" 2>/dev/null >> "${tmpdir}"/zip.log
+
+    # Archive the content of the directory and "spoof" it as an image
+    cd "${tmpdir}/system" || exit
+    7z a "system.zip" -- * >> "${tmpdir}"/zip.log
+    mv system.zip system.img
+    cd ${tmpdir}
 elif 7z l -ba "${romzip}" 2>/dev/null | grep -q "*system.bin*"; then
     echo "bin images detected"
     7z x -y "${romzip}" 2>/dev/null >> "$tmpdir"/zip.log