Use different name for root recipe to child recipies

[Robert Ancell]

Currently each directory in a project contains a file called 'Recipe'. The root recipe is determined by checking if "project.name" is defined.

The advantages of this method are:
- All recipes look equal
- Bake can automatically build the recipe tree

The disadvantages are:
- project.name needs to always be defined even though it's not strictly required for simple recipies
- If you have another root recipe in your tree then a mistake in it can make Bake think it's a child recipe

So a current project might look like this:
Recipe
src/Recipe
data/Recipe

We could switch to:
Recipe
src/Recipe.child
data/Recipe.child

Then it's not ambigious and project.name doesn't need to be defined.