Softlayer-zeep

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- Fix SSL issue on with `TornadoAsyncTransport` (792)
- Fix passing strict keyword in XML loader (787)
- Update documentation

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This is a major release, and contains a number of backwards incompatible
changes to the API.

- Refactor the settings logic in Zeep. All settings are now configured using
the zeep.settings.Settings() class.
- Allow control of defusedxml settings via zeep.Settings (see 567, 391)
- Add ability to set specific http headers for each call (758)
- Skip the xsd:annotation element in the all:element (737)
- Add Settings.force_https as option so that it can be disabled (605)
- Strip spaces from QName's when parsing xsd's (719)
- Fix DateTime parsing when only a date is returned (672)
- Fix handling of nested optional any elements (556)
- Check if part exists before trying to delete it (659)

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- Fix AnyType value rendering by guessing the xsd type for the value (552)
- Fix AnySimpleType.xmlvalue() not implemented exception (644)
- Add __dir__ method to value objects returned by Zeep
- Don't require content for 201 and 202 status codes (613)
- Fix wheel package by cleaning the build directory correctly (634)
- Handle Nil values on complexType with SimpleContent elements (604)
- Add Client.namespaces method to list all namespaces available
- Improve support for auto-completion (537)

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- Add support for tornado async transport via gen.coroutine (530, Kateryna Burda)
- Check if soap:address is defined in the service port instead of raising an
exception (527)
- Update packaging (stop using find_packages()) (529)
- Properly handle None values when rendering complex types (526)
- Fix generating signature for empty wsdl messages (542)
- Support passing strings to xsd:Time objects (540)

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- The XML send to the server is no longer using ``pretty_print=True`` (484)
- Refactor of the multiref support to fix issues with child elements (489)
- Add workaround to support negative durations (486)
- Fix creating XML documents for operations without aguments (479)
- Fix xsd:extension on xsd:group elements (523)

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- Automatically import the soap-encoding schema if it is required (473)
- Add support for XOP messages (this is a rewrite of 325 by vashek)