add digbt engine

Unfortunately, it is quite slow so it is disabled.
Furthermore, the display of number of files is wrong
on digbt.org, so it is not displayed on searx.

searx/utils.py

@@ -237,3 +237,21 @@ def list_get(a_list, index, default=None):
         return a_list[index]
     else:
         return default
+
+
+def get_torrent_size(filesize, filesize_multiplier):
+    try:
+        filesize = float(filesize)
+
+        if filesize_multiplier == 'TB':
+            filesize = int(filesize * 1024 * 1024 * 1024 * 1024)
+        elif filesize_multiplier == 'GB':
+            filesize = int(filesize * 1024 * 1024 * 1024)
+        elif filesize_multiplier == 'MB':
+            filesize = int(filesize * 1024 * 1024)
+        elif filesize_multiplier == 'KB':
+            filesize = int(filesize * 1024)
+    except:
+        filesize = None
+
+    return filesize