Support PHP 5.3

[jkodumal]

The LD PHP library currently uses Guzzle 5.x, which requires PHP 5.4+. Support for PHP 5.3 will require re-implementing GuzzleFeatureRequester with Guzzle 3.8.1

[jkodumal]

A v2 compatible SDK is now available on the php-53 branch and is undergoing final testing and documentation updates.