Implement rule set from Sway

[casserni]

rules taken from
sway

• Operations cannot have both a body parameter and a formData parameter | Error
• Operations must have only one body parameter | Error
• Operations must have unique (name + in combination) parameters | Error (also in swagger)
• Operations must have unique operationId | Error
• Path parameters declared in the path string need matching parameter definitions (Either at the path-level or the operation) | Error
• Path parameter declarations do not allow empty names (/path/{} is not valid) | Error
• Path parameters definition (Either at the path-level or the operation) need matching paramater declarations | Error
• Path strings must be (equivalently) different (Example: /pet/{petId} and /pet/{petId2} are equivalently the same and would generate an error) | Error
• Paths must have unique (name + in combination) parameters | Error
• Referenceable definitions should be used by being referenced in the appropriate way | Warning
• References must point to existing documents or document fragments | Error
• The default property for Schema Objects, or schema-like objects (non-body parameters), must validate against the respective JSON Schema | Error
• Circular composition/inheritance for Schema Objects is not allowed (You can have circular references everywhere except in composition/inheritance.) | Error
• The items property for Schema Objects, or schema-like objects (non-body parameters), is required when type is set to array (See Schema does not enforce requirement of array items object OAI/OpenAPI-Specification#174) | Error
• The required properties for a Schema Object must be defined in the object or one of its ancestors | Error

[casserni]

Closing after combined with #16