Add gox package

packages/gox.rb

+require 'package'
+
+class Gox < Package
+  description 'A dead simple, no frills Go cross compile tool.'
+  homepage 'https://github.com/mitchellh/gox'
+  version '0.3.0'
+  source_url 'https://github.com/mitchellh/gox/archive/v0.3.0.tar.gz'
+  source_sha256 '29dc6b689f670a5444cc54cd9111549ccb01501901bc9197d0e1325a35157802'
+
+  depends_on 'go'
+
+  def self.install
+    system "mkdir -p #{CREW_DEST_DIR}/usr/local/bin"
+    system "go build -ldflags \"-X main.VERSION=v0.3.0\" -o #{CREW_DEST_DIR}/usr/local/bin/gox"
+  end
+end