Ability to access zipkin_context when using zipkin_span as a decorator

[jdb8]

I like being able to use zipkin_span as a decorator, but it means that I currently can't use update_binary_annotations without converting it to a contextmanager, since I need access to the zipkin_context variable.

E.g. from the docs:

def some_function(a, b):
    with zipkin_span(
        service_name='my_service',
        span_name='some_function',
        transport_handler=some_handler,
        port=42,
        sample_rate=0.05,
    ) as zipkin_context:
        result = do_stuff(a, b)

        # Can add stuff here!
        zipkin_context.update_binary_annotations({'result': result})

vs.

@zipkin_span(
    service_name='my_service',
    span_name='some_function',
    transport_handler=some_handler,
    port=42,
    sample_rate=0.05,
)
def some_function(a, b):
    result = do_stuff(a, b)

    # No access to zipkin_context :(
    zipkin_context.update_binary_annotations({'result': result})

Perhaps a way to solve this would be to add a flag to zipkin_span such as inject_context, which would pass the zipkin_context object to the wrapped function? Then my some_function could receive it as a kwarg.