Adding a command to center metadata

Inspired by Michael Thompson's discussion [here](https://groups.google.com/group/pandoc-discuss/msg/9bba02be44051acc?).

Commands/Center Pandoc Metadata.tmCommand

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>beforeRunningCommand</key>
+	<string>nop</string>
+	<key>command</key>
+	<string>#!/usr/bin/env ruby
+
+meta = 1
+
+ARGF.each do |line|
+    if line =~ /^%/ &amp;&amp; meta 
+        line.slice!(/%\s+/)
+        line = line.chomp.center(78)
+        line.slice!(/\s+$/)
+	   puts "%" + line
+    else
+	    meta = 0
+	    puts line.chomp
+    end
+end
+</string>
+	<key>input</key>
+	<string>document</string>
+	<key>name</key>
+	<string>Center Pandoc Metadata</string>
+	<key>output</key>
+	<string>replaceDocument</string>
+	<key>scope</key>
+	<string>text.html.markdown.pandoc</string>
+	<key>uuid</key>
+	<string>07B9D09D-B6A6-42CE-9D98-0586B34A0411</string>
+</dict>
+</plist>

info.plist

@@ -128,6 +128,7 @@
 		<string>8A4B83DD-08A2-46ED-9219-78AAD9A797B0</string>
 		<string>0E35F798-452C-4D7A-8E67-3741F684C43B</string>
 		<string>56146758-265F-4F83-8322-B77A03E76DB1</string>
+		<string>07B9D09D-B6A6-42CE-9D98-0586B34A0411</string>
 		<string>0AD3F1A6-18CD-459E-90F3-D216F6DC2F62</string>
 		<string>9D2B64FF-F35F-428B-8751-67BE205EEDE4</string>
 		<string>D8A2538F-BA09-42BB-AE66-8EF2E1EFA7D8</string>