build: installed Moq(v4.2.1402.2112) in Experiment.XunitUnitTest.
refactor: applied the Mock.Of method to simplify setup phrase.
dev: fixed null reference exception thrown if an inner exception of

TargetInvocationException is null.
build: removed the unused reference 'Moq' to Experiment.AutoFixture.
refactor: rearranged the order of the tests.
build: updated moq to v4.2.1402.2112.
dev: fixed that ReferenceCollector does not collect references to

custom attributes.
dev: modified the unnecessary protected member to private.
docs: added release notes for v0.22.4.
refactor: removed unused using directives.
style: added one indentation.
dev: fixed that RestrictiveReferenceAssertion does not throw when

unused reference is specified.
refactor: renamed the tests to clarify.
dev: fixed that IndirectReferenceAssertion does not ignore verifying

unexposed(private/internal) members.
build: increment patch version,

to indicate that this fixes some issues releated to idiomatic
reference assertions.