Replace Openstruct with Hashie::Mash

I rigged this up for I project I was working on, and I though you might be interested.

It replaces using  `OpenStruct` with a `Hashie::Mash` (see https://github.com/intridea/hashie), an extension of a standard Hash that, among other things, allows Object-style dot notation.  

Happy to accept feedback for tweaking.