Added macro parameters into context

If one uses a contextfunction inside a macro, any parameters passed to the macro do not have access to those parameters in the "context", so something similar to the following fails to work as expected.
    
```python
    from jinja2.utils import contextfunction
    
    @contextfunction
    def mycontextfunction(ctx):
        return jinja_env.getattr(ctx, 'a')

    jinja_env.globals.update({ 'mycontextfunction' : mycontextfunction })
```

    {% macro foo(a,b) %}
        {{ mycontextfunction() }}
    {% endmacro %}