WIP: Refactor on top of capistrano v3

(this pull request might be better made against a v3 branch, but I am not able to create one ;) @willdurand)

Capistrano v3 [was announced][1] in June and has many improvements that allow for capifony to be a much simpler layer on top of some already powerful tools.

v3 is still undergoing development and as such some current features in capifony are not possible however this pull request has implemented the most basic capifony features for deploying a Symfony 2 app and is hopefully a decent enough starting point.

This is a good opportunity to cut some of the cruft from capifony (Symfony 1 and `bin/vendors`) and make it a tool that is a little easier to use and more importantly maintain.

Check out the [composer task][3] or the [symfony console task][4] as examples of just how simple v3 makes some of the previously verbose functionality in capifony.

I have written a [changelog][2] that details the changes I have made so far.

[1]: http://www.capistranorb.com/2013/06/01/release-announcement.html
[2]: https://github.com/peterjmit/capifony/blob/capistrano-v3/CHANGELOG%20(v3).md
[3]: https://github.com/peterjmit/capifony/blob/capistrano-v3/lib/capistrano/tasks/composer.rake
[4]: https://github.com/peterjmit/capifony/blob/capistrano-v3/lib/capistrano/tasks/symfony_console.rake