Added Dialog Functionality

[jroodman]

I realized being able to send Dialog Directives had not yet been added into Alexa-rubykit. As this is something I want to include in my app, I took it upon myself to add them.

There are 4 distinct functions added to the response class, one for each type of dialog directive that can be given.

Tests are also included, they use the same formatting as the rest of the project.