Updates to make ready for 2.0 release

- Almost 100% test coverage, see my RFC below for what remains
- Made Symfony 2.3 the minimum requirement

### TODO

- update readme

### RFC

I'd like some feedback on the following issue:

The command is currently `ContainerAware`.  This makes it a pain to test... I would like to make it a service and tag it with `console.command`.  This requires symfony 2.4... We wouldn't need to bump the entire bundle's requirement to 2.4 - you just can't use the command in 2.3.  What do you think?

Any other feedback would be appreciated.