Adding windows go agent recipe

- [ ] @sneal Please review and make recommendations as needed.  Be harsh with me so I can get better at this.
Stylistically I'd prefer to avoid the else statement

```ruby
download_url = node[:go][:agent][:download_url]
if !download_url
  major_ver = node[:go][:version].split('-', 2).first
  download_url = "http://download01.thoughtworks.com/go/#{major_ver}/ga/go-agent-#{node[:go][:version]}-setup.exe"
end
```