[C2hs] A new kind of output marshallers *- (patch attached)

[Manuel M T Chakravarty]

Hi Einar,

> When wrapping libraries that return error codes from functions
> a monadic output marshaller that does not return a value is
> very useful. This implements *- output marshallers that take
> the value and consume it, but don't return a result.
> 
> This is used like:
> 
> foo_error_t foo_something(random, arguments);
> 
> type Err = {#type foo_error_t#}
> 
> {#fun {`Foo', `Bar'} -> `()' handleError*- #}
> 
> handleError :: Err -> IO ()
> handleError ...

Yes, that certainly makes sense.  Thanks for also updating the
documentation!

I have pushed the patch into the public repo.  Thanks for the
contribution.

Cheers,
Manuel