Add no_code_generation and stop_on_failure to config

fixes issue #352

This adds the following options to `phpspec.yml'

```yaml
no_code_generation: true
stop_on_failure: true
```
``stop-on-failure`` is not an argument. It is a ``--stop-on-failure`` option of the command. Arguments are not the same than options in term of a CLI. The wording is confusing in your step