Add remaining `Parameter` properties

Added remaining Parameter properties. These were added under a new Parameter.Schema type because they are not applicable if a Content.Map is used instead of a JSONSchema.

⚠️ Breaking Changes ⚠️
Some restructuring was done when nesting Parameter's JSONSchema under a new Parameter.Schema type.

Ease-of-use improvements

Focused on making declarative OpenAPI documents easier to write in Swift.

⚠️ Breaking Changes ⚠️
A number of changes to function/initializer arguments or argument names were made. Some of these are breaking and others are not but all of them make declarative document definitions cleaner.

Add convenience constructors for `Parameter.schemaOrContent`

0.5.4

Add convenience constructors for Parameter schemaOrContent

Add `trace` HttpVerb case

Add missing HttpVerb.trace case.

Add checks for which case a `Parameter.Location` is in

0.5.2

Add convenience checks for which case a Parameter.Location is in

Add `required` to `Parameter`

0.5.1

Expose Parameter.Location's required property on the Parameter struct

Numerous Additions

Added support for Example Object and with it examples on Components Object and Media Type Object.

Rounded off test coverage of Media Type Object.

Added a number of other small things.

⚠️ Breaking Changes ⚠️
Requires Swift 5.1

Add vendor extensions to Content

Content gets vendor extensions (specification extensions) via a dict that can hold arbitrary additional properties.

Tons of additions, improvements, test coverage, and breaking changes.

⚠️ Breaking Changes ⚠️

• PathItem Parameter
• JSONReference
• JSONSchema

Fix annoying warnings and add integer expressibility to status codes.

• Fix annoying warnings from passing nil to string interpolation.
• Add integer expressibility for response status codes and add unit tests for Response file.