Add "body" validation to OperationTestCase

Also remove unused "postFields" validation.
Add base CreateOperationTestCase
Add generic Decorator class
Add DecoratedRequestVisitor
Add JsonVisitor RequestVisitor
Re-do JsonVisitor
Add new JsonVisitor to RelationshipPlugin
Fix PHP OOM error while processing test coverage
Improve consistency of key order in description
CreateArticle
CreateCase
CreateCompany
CreateCustomer
CreateIntegrationUrl
CreateMacro
CreateTopic
Update project progress in README

Fixes #8.