Remove httparty dependency & monkey patches?

[fschwahn]

I'm trying to reduce the dependencies of my projects, and googl has a dependency on httparty, but uses almost no functionality of it. I replaced it with net/http in 65 LOC, and all tests remain green.

Also, I removed the monkey patches (to_openstruct and underscore) and replaced them with methods in the Googl::Utils-module.

If you are interested, I can put together PR with these changes.