Fix error with subdirectories

Thank you @excitoon for the PR!

gitignore_parser.py

@@ -78,17 +78,17 @@ def rule_from_pattern(pattern, base_path=None, source=None):
     # A slash is a sign that we're tied to the base_path of our rule
     # set.
     anchored = '/' in pattern[:-1]
-    if pattern[0] == '/':
+    if pattern[:1] == '/':
         pattern = pattern[1:]
-    if pattern[0] == '*' and len(pattern) >= 2 and pattern[1] == '*':
+    if pattern[:2] == '**':
         pattern = pattern[2:]
         anchored = False
-    if pattern[0] == '/':
+    if pattern[:1] == '/':
         pattern = pattern[1:]
-    if pattern[-1] == '/':
+    if pattern[-1:] == '/':
         pattern = pattern[:-1]
     # patterns with leading hashes are escaped with a backslash in front, unescape it
-    if pattern[0] == '\\' and pattern[1] == '#':
+    if pattern[:2] == '\\#':
         pattern = pattern[1:]
     # trailing spaces are ignored unless they are escaped with a backslash
     i = len(pattern)-1

tests.py

@@ -111,6 +111,13 @@ def test_single_asterisk(self):
         self.assertTrue(matches('/home/michael/directory'))
         self.assertTrue(matches('/home/michael/directory-trailing/'))
 
+    def test_ignore_all_subdirectories(self):
+        matches = _parse_gitignore_string('**/', fake_base_dir='/home/michael')
+        self.assertFalse(matches('/home/michael/file.txt'))
+        self.assertTrue(matches('/home/michael/directory/'))
+        self.assertTrue(matches('/home/michael/directory/file.txt'))
+        self.assertTrue(matches('/home/michael/directory/subdirectory/'))
+
 
 def _parse_gitignore_string(data: str, fake_base_dir: str = None):
     with patch('builtins.open', mock_open(read_data=data)):