Adds the reference to Rui within the metadata.
Adds the LinkForNextCheck property to the IRunnableCheck interface + related tests.
Refactors the extensibility part; few renaming on the interfaces, methods and properties (e.g.: IRunnableCheck-->IChecker; IRunnableStructCheck-->IStructChecker)

Adds tests on the extensibility for struct to end the support of IStructCheck linkage.
Fixes the HowToAddANewAssertion.md + refactors the extensibility.
Updates the version number.
Updates the release note.