Made Image Cache a PHP 5.3+/PSR-2 compliant package

- Fixed indentation and other coding style details to match the PSR-2 standard (see https://github.com/php-fig/fig-standards/blob/master/accepted/fr/PSR-2-coding-style-guide.md)
- Added a namespace (also required by PSR-2) and modified documentation, composer.json and test script accordingly
- Changed the required version of PHP to 5.3.0 and fixed a couple minor issues (lack of a datetime zone definition in the test script, function return value passed directly as reference...) to avoid notices and warnings appearing on PHP 5.3 and above

- Suggestion : autodetect the current path in the test script ? I had to change it when testing my changes, as I guess http://test is some local domain configured on your own working station