update markdown/help header format

Since gitiles recommends using # headers over ---/=== underlines,
change the manifest-format.md over and all our help texts.

Change-Id: I96391d41fba769e9f26870d497cf7cf01c8d8ab3
diff --git a/subcmds/help.py b/subcmds/help.py
index 9bb4c8c..67a225e 100644
--- a/subcmds/help.py
+++ b/subcmds/help.py
@@ -107,15 +107,13 @@
 
         self.heading('%s', heading)
         self.nl()
-
-        self.heading('%s', ''.ljust(len(heading), '-'))
         self.nl()
 
         me = 'repo %s' % cmd.NAME
         body = body.strip()
         body = body.replace('%prog', me)
 
-        asciidoc_hdr = re.compile(r'^\n?([^\n]{1,})\n([=~-]{2,})$')
+        asciidoc_hdr = re.compile(r'^\n?#+ (.+)$')
         for para in body.split("\n\n"):
           if para.startswith(' '):
             self.write('%s', para)
@@ -125,19 +123,8 @@
 
           m = asciidoc_hdr.match(para)
           if m:
-            title = m.group(1)
-            section_type = m.group(2)
-            if section_type[0] in ('=', '-'):
-              p = self.heading
-            else:
-              def _p(fmt, *args):
-                self.write('  ')
-                self.heading(fmt, *args)
-              p = _p
-
-            p('%s', title)
+            self.heading(m.group(1))
             self.nl()
-            p('%s', ''.ljust(len(title), section_type[0]))
             self.nl()
             continue