Introduce Thor

I've ported all rake tasks to thor.

Since now you can use resque bin:

`$ bundle exec resque work -q high`

I tried to change as less as possible in tasks itself. Further refactoring of these will be subject to another PR.

It's generally good to go, few small things missing:

* [x] Figure out verbose stuff (https://github.com/defunkt/resque/pull/858#issuecomment-15026457)
* [x] Add --config option to pass yaml with config directly
* [x] Update examples
* [x] Add --redis && --namespace global options
* [x] Keep rake tasks backwards compatible 

I should complete this in following days (tomorrow hopefuly).

:cake: