Add snap package

packages/snap.rb

+require 'package'
+
+class Snap < Package
+  description 'Server stack which includes sqlite, nginx and php'
+  homepage ''
+  version '1.0'
+
+  is_fake
+
+  depends_on 'nginx'
+  depends_on 'sqlite'
+  depends_on 'php' unless File.exists? "#{CREW_PREFIX}/bin/php"
+end