add 'U' conversion for format strings to unquote their content

(#74)

gallery_dl/util.py

@@ -284,6 +284,7 @@ class Formatter():
     - "u": calls str.upper
     - "c": calls str.capitalize
     - "C": calls string.capwords
+    - "U": calls urllib.parse.unquote
     - Example: {f!l} -> "example"; {f!u} -> "EXAMPLE"
 
     Extra Format Specifiers:
@@ -298,6 +299,7 @@ class Formatter():
         "u": str.upper,
         "c": str.capitalize,
         "C": string.capwords,
+        "U": urllib.parse.unquote,
         "s": str,
         "r": repr,
         "a": ascii,

test/test_util.py

@@ -145,6 +145,7 @@ class TestFormatter(unittest.TestCase):
     kwdict = {
         "a": "hElLo wOrLd",
         "b": "äöü",
+        "u": "%27%3C%20/%20%3E%27",
         "name": "Name",
         "title1": "Title",
         "title2": "",
@@ -157,6 +158,8 @@ class TestFormatter(unittest.TestCase):
         self._run_test("{a!u}", "HELLO WORLD")
         self._run_test("{a!c}", "Hello world")
         self._run_test("{a!C}", "Hello World")
+        self._run_test("{a!U}", self.kwdict["a"])
+        self._run_test("{u!U}", "'< / >'")
         self._run_test("{a!s}", self.kwdict["a"])
         self._run_test("{a!r}", "'" + self.kwdict["a"] + "'")
         self._run_test("{a!a}", "'" + self.kwdict["a"] + "'")