Use buck rule for ReleaseNotes instead of Makefile

This eliminates the last Makefile in our code base.

Also change the section style within ReleaseNotes from asciidoc style to
asciidoctor style.

Also I feel that put images/link.png under ReleaseNotes and deal with
all the resource packing is too stupid, so I used the unicode emoji
instead of the picture ("🔗"). If this is too crazy, we can also use "#"
instead :) This also affects documentation rendering.

Other side effects:

1. The css of release notes switched from default asciidoc css into
default asciidoctor css.
2. The section anchors for ReleaseNotes/index.html changed from "2_13"
to "s2_13", because asciidoctorj is unhappy with anchors without
letters.

Change-Id: I4adf2ce090385cc6b699445012f10a009892aaac
diff --git a/ReleaseNotes/ReleaseNotes-2.2.0.txt b/ReleaseNotes/ReleaseNotes-2.2.0.txt
index 5938f66..5cc54f9 100644
--- a/ReleaseNotes/ReleaseNotes-2.2.0.txt
+++ b/ReleaseNotes/ReleaseNotes-2.2.0.txt
@@ -1,12 +1,10 @@
-Release notes for Gerrit 2.2.0
-==============================
+= Release notes for Gerrit 2.2.0
 
 Gerrit 2.2.0 is now available:
 
 link:https://www.gerritcodereview.com/download/gerrit-2.2.0.war[https://www.gerritcodereview.com/download/gerrit-2.2.0.war]
 
-Schema Change
--------------
+== Schema Change
 *WARNING:* Upgrading to 2.2.0 requires the server be first upgraded
 to 2.1.7, and then to 2.2.0.
 
@@ -21,11 +19,9 @@
 Git repository. The init based upgrade tool will automatically
 export the current table contents and create the Git data.
 
-New Features
-------------
+== New Features
 
-Project Administration
-~~~~~~~~~~~~~~~~~~~~~~
+=== Project Administration
 * issue 436 List projects by scanning the managed Git directory
 +
 Instead of generating the list of projects from SQL database, the
@@ -52,11 +48,9 @@
 The Access panel of the project administration has been rewritten
 with a new UI that reflects the new Git based storage format.
 
-Bug Fixes
----------
+== Bug Fixes
 
-Project Administration
-~~~~~~~~~~~~~~~~~~~~~~
+=== Project Administration
 * Avoid unnecessary updates to $GIT_DIR/description
 +
 Gerrit always tried to rewrite the gitweb "description" file when the