Backward compatibility to OpenAPI v3.0

[RobinTail]

This PR might fix the issue #83 by making several types and the builder class generic.
The generic types depend on the new type OpenAPIVersion that differentiates 3.0.x and 3.1.x.

Some properties like exclusiveMinimum and exclusiveMaximum become either boolean (3.0.x) or number (3.1.x) depending on the OpenAPI version.

Since the default OpenAPI version is 3.0.0 (though it can be determined automatically from the openapi parameter), these changes might be considered as breaking to the current major version of the library.

I'm open to any suggestions and recommendations on how I could improve this PR to support both 3.0 and 3.1.

Closes #83

[RobinTail]

@pjmolina && @jonluca , please review

[pjmolina]

Thanks for the proposal @RobinTail. Formally, it seems to me pretty correct.

However, I have a concern about the maintainability problems it can introduce in the long term if we decide to follow this path:

• The PR impacts in many small places spreading type versioning info in all the object model.
• For future changes, it can only get worse and growing and we will be forced to follow this pattern.
• Someone can forget how to apply this pattern ruining it all, making the lib more fragile.

In this particular case, the issue was to fix exclusiveMaximum & exclusiveMinimum typing.

The pragmatic alternative (lest cost in terms of maintenance) is: to type both exclusiveMaximum & exclusiveMinimum as number | boolean to support both 3.0.x and 3.1.0. This is what I feel we should do here, so far.

The rationale here is, an Openapi Validator will validate and reports full errors on the document.
We can always pass the validator this later, but at building time we are no constraining both approaches.
Our goal here is to be able to build the doc (not necessarily to validate). The validator will tell us if valid (needed in any case because it will check for more constraints that the ones enforced by the type-systems).

Thoughts?

[RobinTail]

@pjmolina ,

yes. That make sense. Thank you for sharing.
I'll prepare another PR according to the concept you described.

[RobinTail]

Instead of this — #85