dev: create private FirstClassCommand.
dev: address exceptions thrown from NaiveFirstClassTheoremAttribute.
dev: add test to address valid return type of test method.
refactor: change InvalidCastException to ArgumentException.
refactor: extract IsReturnTypeValid method.
dev: add test to ensure that parameterized test is non-acceptable.
dev: address some code analyses.
dev: show explicit message of exception,

thrown when method isn't parameterless
dev: address ensuring the test delegate is static.
refactor: clarify the exception message

The delegate string is not well-format.
dev: add some scenario tests for first class tests.
refactor: improve excepton message.
refactor: remove unnecessary using directive.
Merge pull request #22 from jwChung/exception-handling

Handle exceptions thrown when creating test commands