[HatoholMessageBox] Change the argument specification (But Compatibility of convenient functions are kept).
[HatoholMessageBox] Hide title bar if it is demanded.
[testResult] Fix a problem that sometimes fail a test.

This implementation simply retry to read the file.
[HatoholMessageBox] Set the visibility only to the concerned element.
[HatoholMessageBox][test] Check the visibility of the title bar.
[HatoholMessageBox][test] Clean up.
[HatoholMessageBox][test] Use double quation that is the standard of this project.
[HatoholMessageBox][test] Check the button label.
[testMain] Show errnor on the error.
[MLPL] Add an API description.
[MLPL][StringUtils] Add a broundary check.
[MLPL][StringUtils] Clear the specification of eraseChars().
[HatoholMessageBox] Check the string of the title.
[HatoholMessageBox][test] Add a comment.
[HatoholMessageBox][test] Add a clean up of the test that reset the HatoholDialogObserver.
[HatoholMessageBox][test] Destory the message box element after each test.
[HatoholMessageBox][test] Add a new test: 'specify the title'.
[HatoholMessageBox][test] Add a new test: 'specify the defaultButtonLabel'.
[HatoholMessageBox][test] Clean up by adding a helper function.
[HatoholMessageBox][test] Clean up with a helper function.