Add rst-header-replace script.

CHANGES.rst

@@ -1,3 +1,8 @@
+v7.22.0
+=======
+
+* Added ``rst-header-replace`` script.
+
 v7.21.0
 =======
 

jaraco/develop/rst-header-replace.py

@@ -0,0 +1,26 @@
+import re
+import sys
+
+import autocommand
+
+
+def replace_len(char):
+    def replacer(match):
+        size = len(match.group('heading'))
+        return char * size
+
+    return replacer
+
+
+@autocommand.autocommand(__name__)
+def run(before, after):
+    assert len(before) == 1
+    assert len(after) == 1
+    for line in sys.stdin:
+        repl = re.sub(
+            f'^(?P<heading>({re.escape(before)})+)$',
+            replace_len(after),
+            line,
+            flags=re.MULTILINE,
+        )
+        sys.stdout.write(repl)