Use the new section title style in Asciidoctor.

We previous use the section title style like:

Section level 1
===============

Section level 2
---------------

Which have a problem in Asciidoctor that the number of "="s or "-"s must match
the number of characters in the header exactly, as a result it's easy to make
mistakes while changing the titles. Asciidoctor provides a better style like:

= Section level 1

== Section level 2

So we switched to this style.

Also fixed a bug in replace_macros.py, which will not cause any problem in the
old style.

Change-Id: I811dd7238735d98f662767c17086152cd69aea02
diff --git a/Documentation/pgm-index.txt b/Documentation/pgm-index.txt
index c599462..3bb6182 100644
--- a/Documentation/pgm-index.txt
+++ b/Documentation/pgm-index.txt
@@ -1,5 +1,4 @@
-Gerrit Code Review - Server Side Administrative Tools
-=====================================================
+= Gerrit Code Review - Server Side Administrative Tools
 
 Server side tools can be started by executing the WAR file
 through the Java command line.  For example:
@@ -8,8 +7,7 @@
 
 Tool should be one of the following names:
 
-Tools
------
+== Tools
 
 link:pgm-init.html[init]::
 	Initialize a new Gerrit server installation.
@@ -32,8 +30,7 @@
 version::
 	Display the release version of Gerrit Code Review.
 
-Transition Utilities
-~~~~~~~~~~~~~~~~~~~~
+=== Transition Utilities
 
 link:pgm-LocalUsernamesToLowerCase.html[LocalUsernamesToLowerCase]::
 	Convert the local username of every account to lower case.