Test enhancement

[peter279k]

Changed log

• Let this package require php-5.5+ version at least because php-5.4 is too old and outdated.
• It looks like the ext-openssl is required before php-7.0 version, define the suggested extension to notice the users.
• Initialize Travis CI build. The build log is available here.
• Set the current @covers and @use annotations to do the completed unit tests without warnings.
• Set the different PHPUnit versions to support multiple PHP versions.