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
Add "translations" link to TopicModel
Add CreateArticleOperation
Add CreateCaseOperation
Add CreateCompanyOperation
Add CreateCustomerOperation
Add CreateIntegrationUrlOperation
Add CreateMacroOperation
Add CreateTopicOperation
Update project progress in README

Fixes #8.