dev: introduce NaiveFirstClassTheoremAttribute.
dev: introduce ITestCase and FakeTestCase.
dev: implement EnumerateTestCommands,

of NaiveFirstClassTheoremAttribute.
refactor: improve the EnumerateTestCommands method.
refactor: introduce local variable to simplify.
refactor: change signature of ConvertToTestCommand

ITestCommand ConvertToTestCommand(IMethodInfo method) ->
ITestCommand ConvertToTestCommand(IMethodInfo method, ITestFixture testFixture)
dev: introduce the FixtureFactory propety.
dev: add guard clause to EnumerateTestCommands.
dev: impelement FixtureType.
refactor: fix exception type.
dev: address some code analysis warnings.
dev: address guard clauses in constructors.
dev: address creating test fixture for each test-case.
Merge pull request #20 from jwChung/first-class-tests

Implement NaiveFirstClassTheoremAttribute