API operation mapping structure

Python based OpenStack API binding tools are structured on a resource base, where every API resource is a class/object having multiple methods for the resource CRUD and other operations. Moreover microversion differences are also being dealt inside this single object. This causes method typing being problematic and not definite (i.e. when create and get operations return different structures or microversions require modified types).

Since Rust is a strongly typed programming language the same approach is not going to work (neither this approach proved to be a good one). Every unique API call (url + method + payload type) is represented by a dedicated module (simple Enum are still mapped into same module). All RPC-like actions of OpenStack services are also represented by a dediated module. Also when the operation supports different request body schemas in different microversions it is also implemented by a dedicated module. This gives user a better control by using an object with definite constraints explicitly declaring support of a certain microversion.