Split gir into lib and binary

[GuillaumeGomez]

cc @EPashkin @sdroege @federicomenaquintero

[EPashkin]

@GuillaumeGomez Thanks. Slightly bad that it mixed with errorchain removal, but it looks good for me.

Sorry but after #583 it need another fix

  --> src\xmlparser.rs:95:51
   |
95 |     pub fn attr_from_str<T>(&self, name: &str) -> Result<Option<T>>
   |                                                   ^^^^^^^^^^^^^^^^^ expected 2 type arguments

[GuillaumeGomez]

Ah right. At some time I just removed a few things and then I went up until removing all of error-chain... More like a side-effect than a main focus. 😆

[EPashkin]

Thanks.

[sdroege]

And next step is to move to failure? Not that it's really needed here, all errors are stringly-typed :)

[GuillaumeGomez]

I'd prefer to not use anything for error handling until we have a real need for it. :)