Add gifsicle package

packages/gifsicle.rb

+require 'package'
+
+class Gifsicle < Package
+  description 'Gifsicle is a command-line tool for creating, editing, and getting information about GIF images and animations.'
+  homepage 'http://www.lcdf.org/gifsicle/'
+  version '1.89'
+  source_url 'https://github.com/kohler/gifsicle/archive/v1.89.tar.gz'
+  source_sha256 '9b19ff8d50d88af5a5151eaf9e62beb1dd5b72002e7b7cc3aec9b385780e6b83'
+
+  def self.build
+    system './bootstrap.sh'
+    system './configure --without-x --disable-gifview'
+    system 'make'
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end