Add a #servicename method hooked on Wasabi::Document#servicename.

[keltia]

This is the link between Savon and Wasabi (see savonrb/wasabi#22).
Can be overridden by global options.

[rubiii]

thanks @keltia. two things:

1. as the service name is not used internally, why would you need a global overwrite?
2. i'm not sure whether the #servicename method should be exposed through the client or if it would make sense to add another "layer" and exposes some kind of service object which can be asked for its name and operations. give me a moment to think about this.

[keltia]

@rubiii I'm not sure the client interface is the right way to expose no but as @wsdl has no accessor, I have no choice for now. I'm not sure about the global overwrite, it just seems interesting to me to be able to change it. My goal is, as I told on Twitter, to be able to generate some kind of proxy class for the service and having the service name available is better than trying to guess it through the filename in my personal case.

[rubiii]

@keltia i understand. so you would be fine with removing the global option, because all your services have a name?!

[rubiii]

merged your changes, renamed the method to service_name and pushed the changes to master.
this will be released with v2.2.0. thanks @keltia!