"Getting started" update

Merge pull request PHP-DI#174 from mnapoli/4.3

4.3

Fixed test for PHP 5.3 compatibility

Merge pull request PHP-DI#178 from mnapoli/php-5.3.3-support

PHP 5.3.3 support

Merge pull request PHP-DI#165 from mnapoli/4.2

4.2

Code simplification in the definition dumper/Debug object

Fixed a bug that would cause conflicts between DI\ContainerInterface …

…and Interop\Container\ContainerInterface when included in a specific order

Merge pull request PHP-DI#155 from mnapoli/4.1

4.1

Added PHP 5.6 to the tests

Improved documentation for migrating to v4