Bump Requirements to PHP 5.4 for Sentry 3

1. Laravel is doing it, so we're not losing a huge potential market.
2. PHP 5.3 is end of life.
3. Using traits will allow us to simplify the codebase...a lot.
4. All the other good stuff in PHP 5.4

Before I merge this into develop, if you have objections, speak now and forever hold your peace.