Fix async requests

The gem doesn't work with a new Rails app created with the latest versions of Rails and Ruby (Rails 4.0 and Ruby 2.0) because the patch for `Net::HTTP` used for async requests doesn't build the HTTP request properly.

This changes the `LogClient` class to use the [SuckerPunch](https://github.com/brandonhilkert/sucker_punch) gem for async. It's designed for exactly this sort of case and avoids having to tinker with core classes. 

I've been using this version in production and it has been working fine. If this change is acceptable I can either add to it or follow it up with a few spec tests to verify and also the removal for the `Net::HTTP` change.