Use step-down rule for of the order of function policy (#77)

* Remove current fct ordering policy

* Rephrase to use the step-down rule

* Lint

CONTRIBUTING.md

@@ -669,11 +669,14 @@ Without a logical order, it can be difficult to follow modules and classes as
 the number of functions or methods on them grow increasing the maintenance
 burden of the code.
 
-On modules, where a function depends on another function, the dependent function
-should be listed after the function it depends on. This means that the functions
-with the fewest dependencies on other functions in the module should be listed
-first. Functions should also be grouped logically. If functions have a similar
-purpose, they should be grouped together.
+Functions should be ordered according to the 
+["step-down"](https://dzone.com/articles/the-stepdown-rule) rule.
+This means that a module should be readable from top to bottom, 
+with functions ordered by level of abstraction, from general to specific. 
+A calling function should always be above the called function. 
+Functions should also be grouped together logically. If functions have a
+similar purpose, they should be grouped together.
+
 
 On classes, the `__init__` method should come first followed by any other
 factory methods, such as `from_charm`. The rest of the methods on a class should