to preserve unicity of "atoum cli arguments", I use the name of the argument as a key (i.e: --bootstrap-file).
If the value is null, we're dealing with non-value option like --test-all which has no value. 
If the value is not null we're dealing with a classic option: --bootstrap-file="path"

Every key of this array are then inlined with the getAtoumArguments() to match the syntax that the runner expects:
```php
array('--test-all', '--bootstrap-file', '/path/to/bootstrap', ...)
```