Fixes, updates, changes

[MisterDA]

This huge PR is an attempt at updating the code with some fixes, making it work with newer dependencies, and more Swagger specs. A major change is that it uses Ppxlib to generate the AST instead of outputting strings of OCaml code, and it most cases we can use metaquot to actually write OCaml code instead of manipulating the AST. I've also added tests using Kubernetes and Docker swagger specs which show that this PR does not regress. There's a handful of fixes for the code generation: module names, swagger.atd fixes.

We're still missing however support for allOf composition and inheritance.