PlanOut PHP Port

Woooo it's finally here! :smile: The release currently includes:
- [x] full support and unit tests for random operators, experiments, and namespaces
- [x] support for creation of experiments and namespaces using either PHP 5.4 "traits" or standard subclassing
- [x] native support for any [PSR-3 compliant logger](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-3-logger-interface.md). Developers can either utilize existing PSR loggers such as Monolog or write their own simple adapters to make existing logging stacks PSR-3 compliant.

TODO:
- [ ] write in-depth documentation for usage (should essentially mirror the gh-pages branch here)
- [ ] publish repository as a composer package on [Packagist](https://packagist.org/) and update download/usage instructions.

Since I'm submitting this as a PR to include the port as a submodule of the project I'm not sure what the best way to review would be. Feel free to leave comments here or create issues in the master [PHP repo](https://github.com/vimeo/ABLincoln)!

cc @eytan for review + merge
@jacoboliver @adilhashem for updates :smiley: