Add Recipe Subfolders

The goal of the changes is to allow subfolders in the recipes directory. Recipes can now be divided by category, no changes have to be made to the config file to take advantage of this. There cannot be more than one recipe with the same name though. Previously the recipes directory was flat with each recipe exactly one level deep, now the recipes can be categorized by what they are related to with arbitrary depth. As before, recipes cannot contain other recipes.