Add support for PHP 5.2+

`php-stub` requires PHP 5.4 only because of arrays literal notation (`[]`).
While I like the new syntax for declaring arrays I think it's more practical
to support older versions of PHP if it doesn't harm library's functionality.
Besides, I think `array()` is not that ugly.
Support PHP 5.3.2+

It's not easy to build composer powered code in Travis CI server
as only PHP 5.3.2+ boxes provide required tools to do that.
Additionally, Composer itself
[supports php 5.3.2+](https://getcomposer.org/doc/00-intro.md#system-requirements).
So to make support simpler, I suggest supporting PHP 5.3.2+ too.
Make test suite code compatible with php 5.3.2+
Require PHP 5.3.0+ instead of PHP 5.3.2+

For some reason `composer install` command could only
complete successfully if PHP 5.3.0+ is required and not
PHP 5.3.2+. More report here:
https://travis-ci.org/sergeylukin/php-stub/jobs/40252921
Merge pull request #5 from sergeylukin/support-php52

Add support for PHP 5.2+