V3: Pheanstalk namespaced, PSR-1, PSR-2, PSR-4.

This pull-request introduces PHP namespaces, [PSR-4][psr-4] autoload layout, and stricter [PSR-1][psr-1] and [PSR-2][psr-2] adherence.

It's backwards incompatible with 2.x only in its namespaces, path layout and autoloader. The interface and semantics otherwise remain unchanged.

The resulting release will be tagged as v3.0.0 as per http://semver.org/

[psr-1]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-1-basic-coding-standard.md
[psr-2]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md
[psr-4]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader.md