[Soap-Python] Renaming the rpc decorator.

[Chris Austin]

Sometime in the short and confusing history of soaplib the method
decorator @soapmethod was renamed to @rpc in order to support the
previous maintainers vision of creating a generic rpc library based on
the foundations of soaplib.

Currently, the maintainers are looking to re-focus on SOAP and make
soaplib a flexible and eventually complete soap solution for python.
With this in mind one thing we've discussed changing prior to the beta
release is to re-rename @rpc to @soap. But, before we move forward we'd
like to get feedback from the community.

Please speak up if you have an opinion on the matter.

Chris