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

ReleaseNotes/ReleaseNotes-2.2.1.txt

@@ -1,12 +1,10 @@
-Release notes for Gerrit 2.2.1
-==============================
+= Release notes for Gerrit 2.2.1
 
 Gerrit 2.2.1 is now available:
 
 link:https://www.gerritcodereview.com/download/gerrit-2.2.1.war[https://www.gerritcodereview.com/download/gerrit-2.2.1.war]
 
-Schema Change
--------------
+== Schema Change
 *WARNING:* This release contains schema changes.  To upgrade:
 ----
   java -jar gerrit.war init -d site_path
@@ -15,8 +13,7 @@ Schema Change
 *WARNING:* Upgrading to 2.2.x requires the server be first upgraded
 to 2.1.7, and then to 2.2.x.
 
-New Features
-------------
+== New Features
 * Add 'Expand All Comments' checkbox in PatchScreen
 +
 Allows users to save a user preference that automatically expands
@@ -28,8 +25,7 @@ The -b option may be supplied multiple times to ls-project, each
 usage adds a new column of output per project line listing the
 current value of that branch.
 
-Bug Fixes
----------
+== Bug Fixes
 * issue 994 Rename "-- All Projects --" to "All-Projects"
 +
 The name "-- All Projects --.git" is difficult to work with on