[String] StringConvertible inherites boost::equality_comparable to compare with std::string / string literal.
[Test][Android] Add String test suites.
[Error] You may create and compare an ExceptionPtr / AnyFailurePtr with nullptr.
[Error] (refactoring) Hide some ExceptionPtr inline functions into Error.cpp .
[Test] [Android] Add Error test suites, and fix some issues in NDK compiling.
[Error] Add ExceptionPtr::operator==() to itself.
[Error] Add ExceptionCatcher::AnyFailure() and Rethrow().

- CatchException now can recognize an AnyFailure exception.