src/test/mock-sendmail.php: Add more abilities for testing email-sending; use these capabilities in testing our own email-sending methods.
src/array.php: Raise InvalidArgumentException if more than one parameter is provided to 'commonPrefix' function; add relevant test-case.
src/: Add dates.php as a temporary and deprecated way of accessing date-time.php.
Move 'mock-sendmail' script from test/mock/bin/ to a new base-directory, 'bin'; and, update test.php as per this change and to make it use the related functionality now available in the Test\MockEmail module.
src/fs.php: Fix 'isWithinDirectory' and 'isWithinOrIsDirectory' functions; add relevant test-case over 'isWithinDirectory'.