Add a new formula for abook

From abook's website (http://abook.sourceforge.net/):

    Abook is a text-based addressbook program designed to use with mutt mail
    client. Abook runs on Linux, FreeBSD and some other UNIXes.

Probably not the world's most important package, but I can't be the only
mutt-user who missed it.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/abook.rb

@@ -0,0 +1,14 @@
+require 'formula'
+
+class Abook <Formula
+  url 'http://prdownloads.sourceforge.net/abook/abook-0.5.6.tar.gz'
+  homepage 'http://abook.sourceforge.net/'
+  md5 '87d25df96864a7c507a4965e6d1da49d'
+
+  depends_on 'readline'
+
+  def install
+    system "./configure", "--disable-debug", "--disable-dependency-tracking", "--prefix=#{prefix}", "--mandir=#{man}"
+    system "make install"
+  end
+end