extracted the Definition and removed fallbacks

* introduced the Definition object to abstract the hash definition
  returned by the sax parser.

* removed a fallback from the SOAPAction implementation and changed the
  specs to match the soapUI parser.

* removed the no_message_parts fixture and specs, because it's the only
  fixture that relies on a fallback for the input message and not even
  soapUI can parse it. also it was obviously edited by hand, so we can't
  expect it to be valid and base the implementation on specs for it.

* changed specs for the elementFormDefault values to pending, because
  the interpreter doesn't really have one ultimate answer for this, as
  these values belong to one of n schemas.
renamed the Interpreter to Interface

as the logic for interpreting the wsdl has been moved to the Definition
object and interpreting will be moved to a different object as well,
this is just an interface to those objects.
moved a method
renamed SAX to Parser

because that's what it is and the legacy Parser class has been
removed from this branch quite a while ago.
moved type code from Interface to Definition
removed user-specific rspec config
added fuubar as a development dev to the Gemfile
no need to expose the definition any longer
renamed interpreter to interface in specs
removed Interface#element_form_default

it's not ok to only look at the elementFormDefault value of the
first schema. this needs to be handled closer to the actual type.