option to sort data models and api functions

[zijianhuang]

Currently the creation is basically following the order of type and function declaration. However, petstore.yaml v3.0 has all these sorted, while petstoree.yaml v3.0.3 use apparently random order. This make the diff of generated codes between version not readable.

So, have this option in case diff is useful for versioning during development.

[zijianhuang]

Sort namespace, types, properties, methods, surely not enum member.