Updated recipes for Git and Slim, added Simple-Navigation, decoupled Humans and README into their own recipes

My fork contains (and plans further) enhancements to current recipes, new recipes, or decoupling some strangely packaged recipes. These include:

- Adding a recipe for the Simple Navigation gem, including default config files with or without Devise and Omniauth.
- Updates to the Slim recipe. As a Slim template language advocate within the Ruby world, I found the Slim recipe sorely lacking. My updates include more options for configurations, along with additional view templates, etc.
- Updates to the Git recipe, which oddly assumed non-standard branch names.
- Created a separate humans.txt recipe, because the html5 recipe is ridiculously illogical and makes some overly broad assumptions.
- Create a separate README recipe for the same reasons as above, allowing the user to specify which file format they would prefer

More updates to come, including more decoupling of poorly developed recipes, additional enhancements to project configurations, etc.